I’m having the same issue as SPCraft in his post here… the form had no fix either.
https://community.shopify.com/c/shopify-design/cant-seem-to-get-rid-of-a-simple-black-bar-on-my-site/m-p/1659905
I’m using the dawn theme (10.0.0) and when I scroll down on the mobile version I get a sort of transparent sticky black bar that shows up on the bottom of the screen (see attached video).
This issue only happens when I use Firefox on my phone, Chrome seems to work fine. Any suggestions?