How to enable Fix position when scrolling?

Hi

I’m creating a “Back to Top” feature for a website. To design that feature I need to place a button middle of the frame and set the button to “Fix position when scrolling”. Even though I couldn’t have seen that options in Figma. Do you have any ideas, please recommend tips.

PS: I’ve tried scrolling frames in the Prototyping section but none of them worked for my case.
Has Figma eliminated that feature after introducing Sticky Features?

Thanks