1/ This button comes from “Multivendor Marketplace Solution for WooCommerce – WC Marketplace” plugin, read more in the docs of the plugin.
2/ Our theme allows adding a few custom tabs: – a tab common for all the products (Theme Options > WooCommerce > Single product > Tabs) OR when Single Product Builder is activated (you can desctivate it) – 2 custom tabs (common for all the products).
– 1 tab individual for every product (Products > edit product > 8theme Options > Custom tab title and Description https://prnt.sc/K9BZ2RV2XZsR ).
3, 4, 5 / Is Single Product Builder activated on your site? please provide URL of your site.
6, 7/ Do you use Eleemntor of WPBakery? Enable one of these editors for static blocks, then edit the Footer static block.
8/ Check settings of WooCommerce plugin (WC > Settings > Products > Inventory), then enable Show Product Stock Status in Theme Options > WooCommerce > Single Product builder > Add to cart & quantity
9/ Go to Theme Options > search for Buy now button https://prnt.sc/mc-CPtjtn9rV and enable it.
10/ XStore > Sales Booster > Fake Live Viewing
Theme Options > General > Enable Classic Widgets Panel > On, then go to Dashboard > Appearance > Widgets > edit Single product page sidebar https://prnt.sc/8uhDqcebgeMk