Yes, this could be a feature request for a new browser support or a bug request - I did try posting it to the gnupg-devel list, but hit a bounce back.

I currently use the Brave Web browser - a Chromium based browser from brave.com - however, it isn't natively supported by the GPGME integration.

Would it be possible to amend:
https://git.gnupg.org/cgi-bin/gitweb.cgi?p=gpg4win.git;a=blob_plain;f=src/inst-gpgme-browser.nsi;hb=refs/heads/master
to include the relevant sections. I believe using the existing
gpgme-chrome.json file would be appropriate as Brave uses the Google
Chrome Plugin store and the chrome-extension id from Mailvelope is
identical.

The WriteRegStr paths I believe are needed are:

WriteRegStr SHCTX
"Software\BraveSoftware\Brave-Browser\NativeMessagingHosts\gpgmejson"
"" "$INSTDIR\bin\gpgme-chrome.json"

(this does work on my Windows 10 Pro machine with Brave1.39.1.22 Chromium 102)

And for the uninstaller in
https://git.gnupg.org/cgi-bin/gitweb.cgi?p=gpg4win.git;a=blob_plain;f=src/uninst-gpgme.nsi;hb=refs/heads/master
:

DeleteRegKey SHCTX
"Software\BraveSoftware\Brave-Browser\NativeMessagingHosts\gpgmejson"

should do the trick (although I haven't tested it myself)..