I really want to love KeyCloak. I've had really bad experiences with weird uptime bugs and crash loops that kept me from giving it an honest retry over the last couple years.

It also really shows its age, imo. The interface is clunky, roles and groups having overlapping responsibilities is confusing, making custom UIs for it makes me feel ancient, etc.

I really can't complain though. There is simply no alternative that's as open atm. It's also not easy to make one ( I tried :( ).

Showing its age is also a pretty significant plus, for such a critical part of one's infrastructure. That means it's been beat up on and run through the ringer for a decade plus at this point and had lots of chances to fix CVEs and other bugs. Not to say there won't be more, but being older and time-proven for an IdP is a major positive.