This fanlore article has a pretty good start on general fan history from the show: https://fanlore.org/wiki/The_Sentinel

there's probably plenty more than can be added.

I watched the show when it was on UPN and then, I think it ran on SciFi in syndication for a long time.

there were yahoogroups for Burgi and the show... i think there are still bits and bobs of old discussions at https://www.sffchronicles.com/forum/sentinel/ - tho, looking, it's kinda dry and not a lot of discussion happened after a while... (that section was originally part of a forum called ascifi.com that was merged into sffchronicles)