Agree, it would be extremely helpful to be able to use custom/spoofed user agents.
A very useful and popular site (www.archive.fo) recently (as of today) doesn’t recognize Brave as a supported browser.
It would be very helpful to be able to change the User Agent in Brave in settings to present at whatever browser you wished to avoid annoyances like this (and also to remember the settings for the specific pages).
There is a similar topic open, don’t know if we can consolidate Change user agent on Android version