Hello,
this issue has been a thing since forever with Brave.
iCloud Passwords simply work fine, but the iCloud Bookmarks simply don’t work, it says that you have to enable Chrome bookmarks on iCloud Windows app to be able to use them. Well, they are enabled for Chrome and it works there. Reading around Internet, in Apple Forum I just read someone from Apple saying that this is something that Brave must fix because the extension works on another Chromium browsers, so that it’s up to them to fix the compatibility issue.
So I’m here because I really want to use Brave, but I really need the bookmarks from iCloud because on Mac/iPhone I only use Safari and on Windows I’m willing to use Brave.