1) Create a Additional Price attribute from admin area and assign into attribute sets as per your requirement.

Store->Configuration->Attributes: Product->Add New Attribute(Additional Price)

Assign into:

Store->Configuration->Attributes: Attribute Sets(Assign Under Groups->Product Details:additional_price)

2) Then you have to override final price value with following custom module:

app/code/Magemonkeys/SpecialPriceSave/view/frontend/templates/product/price/final_price.phtml

<?php
// @var MagemonkeysSpecialPriceSavePricingRenderChangePriceBox $block
$priceChange = $block->getPriceChange();


// @var MagentoFrameworkPricingPricePriceInterface $priceModel
$priceModel = $block->getPriceType('regular_price');

// @var MagentoFrameworkPricingPricePriceInterface $finalPriceModel

$finalPriceModel = $block->getPriceType('final_price');
$idSuffix = $block->getIdSuffix() ? $block->getIdSuffix() : '';
$schema = ($block->getZone() == 'item_view') ? true : false;
$products = $block->getProduct();
?>

<?php if ($block->hasSpecialPrice() || $block->getFormatedPrice($products->getRrpPrice())): ?>
    
    <span class="special-price">
        <?= /* @escapeNotVerified */ $block->renderAmount($finalPriceModel->getAmount(), [
            'display_label'     => __('On Sale'),
            'price_id'          => $block->getPriceId('product-price-' . $idSuffix),
            'price_type'        => 'finalPrice',
            'include_container' => true,
            'schema' => $schema
        ]); ?>
    </span>
    <span class="next-price">
        <?php 
            $products = $block->getProduct();
            if($products->getRrpPrice()){ ?>
                <span class="rrp-price">
                <?php echo 'RRP'.$block->getFormatedPrice($products->getRrpPrice()); ?>
                </span>
                <span class="all-price-wrp">
                <span class="change-price">
                    <span class="change-price-label"><?= __('save'); ?> </span>
                    <?php $_savePercent = 100 - round(((float)$products->getFinalPrice() / (float)$products->getPrice()) * 100);
                        echo '<b style="color:#ec0101">'.$_savePercent . '% </b>';
                    ?>
                </span> 
                <span class="old-price">
                <?= /* @escapeNotVerified */ $block->renderAmount($priceModel->getAmount(), [
                    'display_label'     => __('WAS'),
                    'price_id'          => $block->getPriceId('old-price-' . $idSuffix),
                    'price_type'        => 'oldPrice',
                    'include_container' => true,
                    'skip_adjustments'  => true
                ]); ?>
            </span>
            </span>

            <?php }else{ ?>
            <span class="all-price-wrp">    
                <span class="change-price">
                        <span class="change-price-label"><?= __('save'); ?> </span>
                            <?= $priceChange; ?>
                    </span>     
                <span class="old-price">
                    <?= /* @escapeNotVerified */ $block->renderAmount($priceModel->getAmount(), [
                        'display_label'     => __('RRP'),
                        'price_id'          => $block->getPriceId('old-price-' . $idSuffix),
                        'price_type'        => 'oldPrice',
                        'include_container' => true,
                        'skip_adjustments'  => true
                    ]); ?>
                </span>
            </span>
        <?php  } ?>
    </span>    

</span>

<?php else: ?>
    <?= /* @escapeNotVerified */ $block->renderAmount($finalPriceModel->getAmount(), [
        'price_id'          => $block->getPriceId('product-price-' . $idSuffix),
        'price_type'        => 'finalPrice',
        'include_container' => true,
        'schema' => $schema
    ]); ?>
    <span class="next-price">
        <span class="change-price">
            <span class="change-price-label"><?= __('save'); ?> </span>
            <?= $priceChange; ?>
        </span>

        <span class="old-price">
            <?= /* @escapeNotVerified */ $block->renderAmount($priceModel->getAmount(), [
                'display_label'     => __('RRP'),
                'price_id'          => $block->getPriceId('old-price-' . $idSuffix),
                'price_type'        => 'oldPrice',
                'include_container' => true,
                'skip_adjustments'  => true
            ]); ?>
        </span>
    </span>
    
<?php endif; ?>

<?php if ($block->showMinimalPrice()): ?>
    <?php if ($block->getUseLinkForAsLowAs()):?>
        <a href="<?= /* @escapeNotVerified */ $block->getSaleableItem()->getProductUrl(); ?>"
           class="minimal-price-link">
            <?= /* @escapeNotVerified */ $block->renderAmountMinimal(); ?>
        </a>
    <?php else:?>
        <span class="minimal-price-link">
            <?= /* @escapeNotVerified */ $block->renderAmountMinimal(); ?>
        </span>
    <?php endif; ?>
<?php endif; ?>

app/code/Magemonkeys/SpecialPriceSave/Pricing/Render/ChangePriceBox.php

<?php
namespace MagemonkeysSpecialPriceSavePricingRender;

use MagentoCatalogPricingRenderFinalPriceBox;
use MagentoCatalogPricingPrice;
use MagentoCatalogModelProductPricingRendererSalableResolverInterface;
use MagentoFrameworkViewElementTemplateContext;
use MagentoFrameworkPricingSaleableInterface;
use MagentoFrameworkPricingPricePriceInterface;
use MagentoFrameworkPricingRenderRendererPool;
use MagentoCatalogPricingPriceMinimalPriceCalculatorInterface;
use MagentoFrameworkPricingPriceCurrencyInterface;
use MagentoFrameworkPricingHelperData as Pricehelper;

/**
 * Catalog category helper
 * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
 */
class ChangePriceBox extends FinalPriceBox
{
    protected $currency;
    protected $priceHelper;

    /**
     * @param Context $context
     * @param SaleableInterface $saleableItem
     * @param PriceInterface $price
     * @param RendererPool $rendererPool
     * @param array $data
     * @param SalableResolverInterface $salableResolver
     * @param MinimalPriceCalculatorInterface $minimalPriceCalculator
     * @param PriceCurrencyInterface $currency
     * @param Pricehelper $priceHelper
     */
    public function __construct(
        Context $context,
        SaleableInterface $saleableItem,
        PriceInterface $price,
        RendererPool $rendererPool,
        PriceCurrencyInterface $currency,
        array $data = [],
        SalableResolverInterface $salableResolver = null,
        MinimalPriceCalculatorInterface $minimalPriceCalculator = null,
        Pricehelper $priceHelper
    ) {
        parent::__construct($context,
            $saleableItem,
            $price,
            $rendererPool,
            $data,
            $salableResolver,
            $minimalPriceCalculator
        );

        $this->currency = $currency;
        $this->priceHelper = $priceHelper;
    }
    /**
     * Return difference in original price and final price
     * @return float
     */
    public function getPriceChange()
    {
        $regularPrice = $this->getPriceType(PriceRegularPrice::PRICE_CODE)->getValue();
        $finalPrice = $this->getPriceType(PriceFinalPrice::PRICE_CODE)->getValue();
        $changePrice = $regularPrice - $finalPrice;

        return  $this->currency->format($changePrice);
    }
    public function getProduct()
    {
        $product = $this->getSaleableItem();  
        return $product;
    }
    public function getFormatedPrice($price)
    {
        return $this->priceHelper->currency($price, true, false);
    }
    
}

3) Create a Catalog Rule for Discount Price with Percentage format:

Marketing->Promotions->Catalog Price Rule

See attached screenshot:
https://tinyurl.com/244sf59t

4) See this results, finally it shows on Category Page and Product Detail Page on frontend side with Saving Different Price:

Category Page:

Product Detail Page: