I was transiting MEX this past Thursday (4.1.21) and can report that the pre-security T1 Lounge is open.
I wasn't even aware of if but I saw on my way to Air France check-in. Since I had 4 hours, stopped in.
Pleasant but meh atmosphere. Excellent staff but the lack of any windows and view to the outside gave the place a bit of a dark, dungeon like feel.
Full report with pics...
The Centurion Lounge at MEX | SFO777