Latest Safari seems to have broken footer positioning.
If you load the latest safari on MacOS, the footer positioning seems to be janky/not correct depending on what you're doing.
My version of Safari:

https://www.openstreetmap.org/edit?editor=id#map=5/38.007/-95.844

Does not repro in Safari 14.0.2. Regression on Safari?

My version of Safari seems to be standard on Bit Sur 11.1
I have reason to believe that this is something to do with the update from Big Sur 11.1 -> 11.4, which seems to be updating Safari from 14.0.x to 14.1.x.
Checked 14.1's release notes and trawled through their bug database, doesn't seem to be anything reported on this already.
It seems that there are other reports on the web of Safari 14.1 breaking stuff. So much so that 14.1 has been removed from other earlier versions of MacOS. More here: https://appleinsider.com/articles/21/05/04/macos-bugs-causing-sporadic-browsing-issues-with-safari-firefox-others
Safari 17.4.1 doesn't move the footer to the top anymore. Instead, when using Safari in split screen, the footer just becomes invisible. But all of its links remain clickable.
The mouse was at the red circle.