First, Try To Recognize Them
If it's been over a year and a half since you last saw this person, chances are they may look a little different. Lockdown was, after all, the perfect time for face lifts, chemical peels, a little work around the eyes, CoolSculpting. Once you've established that this indeed the person you know, don't mention any obvious upgrades (or downgrades) to their look. "Oh my god, hiiiii. You look great!" will suffice.