This is excellent advice, I too used to play with a bunch of friends and they all have left. I joined a new guild right before Shadowlands and its been great to get back into the group content like raiding and rated battlegrounds.
Don’t just join any guild from the guild finder, actually talk to a guild leader/officer and find one that meshes with what you want. If you only want to do normal raids and casual low mythic keys, there’s a guild for that.