i think a button like this wld be useful for threads or long pages where you quickly want to jump to the latest post and itd also be generally useful if you just wanna quickly jump to the top of the page as well

I know many pages have such a floating button in the bottom right. Make it toggle between jumping to top and bottom?

But maybe check if your browser has keybindings for that first. You can also hold the spacebar to scroll to the bottom of a page.

on physical keyboarded devices with these keys, you may use the Home and End keys to scroll to top/bottom. (more people should know about this!!)