I have a similar issue with this one, expect that it happens when editing the bookmark location in the bookmark popup. Using the same browser version on Windows 10. Unfortunately I’m a new user and can’t upload attachments.
I use a resizer application that is designed to anchor window sizes and positions. Brave breaks this setup since it gets into an endless battle whenever a popup requester happens. Brave changes the window size, Zmover (the window size/pos. app) changes it back, Brave notices and puffs up its size and Zmover puts it back, and so on and so on. It’s almost funny if it wasn’t robbing my time.
Apps should NEVER change their window size without some kind of buy-in from the user.