If I change the font size in Chrome's Settings/Appearance panel, the text in the entry box does not scale with the rest of the text on the page. The attached screenshots were done in Chrome Version 92.0.4515.159 (Official Build) (x86_64) on MacOS 11.5.2 (20G95)
Topic on Talk:Talk pages project/Replying/Flow
The reply tool uses the exact same font settings as the normal wikitext editor, and it also does not respect the browser font size.
Opened T289519
Actually, I found existing tasks about this problem:
I'll merge yours into the second one.