Default browser setting not sticking

Browser Version 1.24.85 Chromium: 90.0.4430.212 (Official Build) (64-bit)
OS Version 1.24.85 Chromium: 90.0.4430.212 (Official Build) (64-bit)

If I click ‘Set Default’ in settings, it only lasts until I close the browser, then the ‘Set Default’ button reappears next time the browser is started. If I go into Linux system settings/Preferred Applications the browser isn’t listed as an option, so can’t be selected there. Other application show up in the Preferred Applications lists okay. I then installed Chromium and Firefox as a test, and they both show as options in Preferred Applications, it’s just Brave that fails to be able to set its self as default.

Anyone have a clue why this might be happening?
Chris

I have tried a fresh install twice, with the sams result