Unfortunately, you can't install opera stable, beta and developer at the same time from the repos.
I had to install opera stable 98 from flatpak, beta 98 and developer 100 from the repos, but now I can't upgrade to beta 99 (manually, not in the repos yet) because of conflicting files (see https://forums.opera.com/topic/62356/opera-99-beta/3?_=1684003600733 for details).