Mozilla introduced new profile manager for Firefox somewhere around May. This thing uses new storage format and ignores already existing "old" profiles, except for the default one. Data remains untouched, profiles created in the past are still here accessible by about:profile and if you don't want to use that new profile manager set browser.profiles.enabled entry to false.

From what I've seen around people using the popular customized Firefox variants, like Floorp, Librewolf were surprised by this and not fond of the change.