See https://www.reddit.com/r/operabrowser/wiki/opera/new_profile/#wiki_create_multiple_profiles_for_opera. Those directions are for Windows, but you can use the same --user-data-dir command-line switch on Linux. Try with the deb version of Opera first. Then you can adapt that to the flatpak or snap version of Opera if you use one of them.

For example:

opera --user-data-dir=~/.config/opera/profile2