Get all the attributes which are used in layered navigation in category & search page.

You can get all the filterable attribute list from MagentoCatalogModelResourceModelProductAttributeCollectionFactory class.

As a result, you will get that,

all those attributes which have been used in Layered Navigation status are Filterable (with results) or Filterable (no results).

So, you need to create __construct( ) function for define dependency of Class.

<?php
    private $checkoutSession;

    public function __construct(
        MagentoCatalogModelResourceModelProductAttributeCollectionFactory $productAttributeCollectionFactory
    ) {
        $this->productAttributeCollectionFactory = $productAttributeCollectionFactory;
    }

    public function getFilterableAttributes()
    {
        /** @var MagentoCatalogModelResourceModelProductAttributeCollection $productAttributes */
        $productAttributes = $this->productAttributeCollectionFactory->create();
        $productAttributes->addFieldToFilter(
            ['is_filterable', 'is_filterable_in_search'],
            [[1, 2], 1]
        );

        return $productAttributes;
    }

Now call a function in template file by iterating over a loop to fetch each attribute code,

$getAttributes = $block->getFilterableAttributes();

    foreach ($getAttributes as $attribute) {
        echo $attribute->getAttributeCode();echo "<br>";
    }

You can get all the filterable attribute used for your store.

The Result

    price
    manufacturer
    color
    activity
    style_bags
    material
    strap_bags
    features_bags
    gender
    category_gear
    size
    eco_collection
    performance_fabric
    erin_recommends
    new
    sale
    format
    style_bottom
    style_general
    sleeve
    collar
    pattern
    climate