I’ve been a user of profiles since Firefox was Netscape.  It took me a minute to realize that the feature isn’t toggled on by default.  There’s was no mention of the functionality the the 145 release notes.  It can easily be switched on in about:config by toggling the key browser.profiles.enabled from false to true.  This new profiles functionality seems to be separated from current profiles though.  I was hoping that my existing profiles would just be there.  It could be that’s coming and part of why the feature is currently toggled off by default.  Will be interesting to see how this matures.