On my most recent MEX departure a couple weeks ago, when the check-in area was a complete poopoodoodookaka show and many check-ins were taking 15 to 20 minutes (as I waited the better part of two hours not moving much in line), it didn't look like the agents were paying much attention.

That said, in my AM experience over the past several years (all pre-COVID), the odds are better than not that a check-in agent will ask to see the carry-on and weigh it, and gate agents may be checking around the gate area, and sometimes, while boarding, the agent will take a close look and size/weigh it at the gate.

Also, at one point (although it doesn't seem to be the current case, but you never know when it might reappear) that no one was getting through the MEX T2 security checkpoint without having their hand luggage tagged as permitted.

All of my AM experience has been in premium cabin flying - so while the permitted weight might have been higher, it didn't stop them from enforcing the rules du jour.