Unable to apply Fixed position for floating button in prototype. Option is greyed out without explanation.

Hey ​@Viktor Sherepa , thanks for reaching out about this!

I understand you're trying to assign a fixed scroll position to an object, but the option is grayed out. I totally get how frustrating that must be!

And thanks for your feedback about the lack of in-app explanation – it would definitely be helpful to see why you can't apply that when you try selecting a fixed position. I'll pass that thought along to the appropriate team.

Could you please check if the object you're trying to assign fixed scroll position is inside a frame with Auto Layout applied?

As mentioned in our Help Center article below, you can't assign a fixed scroll position to any objects within an Auto Layout frame unless that object has absolute position.
Prototype scroll and overflow behavior > Apply scroll position to objects within a frame > Fixed

If what you're experiencing is different from what's described in our Help Center article, please submit a bug report by following this guide: Submit a bug report. This will allow our team to take a closer look at what's going on.

Thanks again for reaching out! We appreciate you letting us know about this.