I'm trying to find vacation destinations in the Caribbean/Mexico that are "back to normal" friendly.
That is, no vaccines, no testing, no quarantining, no face masks, no social distancing etc.

I read recently that Mexico has lifted the main restrictions but still requires face masks.
Is this true?
Say you are in Cancun airport? Face masks required?
How about your resort/hotel etc.?

All that depends on where you're going in Mexico. Mexico has never had any vaccine or testing requirements. They were the only country that never closed, and never had any restrictions to enter. But required masks. Yes, they recently lifted the mandates in regard to wearing masks in airports and public transportation "overall", but private operated stores, clinics, hospitals, hotels and restaurants can have their own restrictions. Therefore, the entire country is NOT mask free if that's what you're asking.

That's not quite what I was asking.
I'm in Canada and roughly 25% of the population is still wearing masks.
But they are wearing them of their own volition.

I would like to know if hotels/resorts, airports, force people to wear masks?
And do they have medical exemptions, and if so how is that recognized?

Force? Like China had done? No, because most people abide by the request and signage.

Not quite like China, but in a way where you would have no choice but to leave the property if you didn't obey.
What happens when the minority don't abide?

During the pandemic, the restrictions and masking requirements were enforced at the State and/or local level depending on the severity of cases according to the color coded system developed by state officials. At the Federal level, Mexico didn't have any restrictions as this was all enforced at the State and/or local level, some of which were bizarre.

At this point, the masking requirement has been left to each establishment.

It depends if the signage is just a leftover from the days of the pandemic or they actually enforce it.
I have been a few hotels where face masks were required according to the signage, I complied during the check-in but stopped using it and the staff didn't bother me or other guests not using mask. I'm not sure why the signage is still there if they aren't doing anything about it. Airports also fall into the "it depends" category. This within a span of 2 months.

Mexican flagged airlines require the usage of face masks, as apparently this is still a requirement by Mexican aviation law according to the announcements.
Foreign flagged airlines will make announcements, if an particular Mexican airport requires face mask.

I was in Oaxaca a month ago, and I was shocked by how much masking was going on. It was mostly on public transportation (which is fine) and tourist attractions, including outdoor ones (such as the ethnobotanic garden - which to me made zero sense.) The hotels where I stayed generally had signs up saying masking was mandatory, but when I asked staff if that was still valid, they said not to worry about it. Lots of stores still required masking - and I can't count how many places forced me to take hand sanitizer before I stepped in - but some didn't. I would say that many locals also walked around with masks on while outside, and I ended up doing the same a lot because it was just a hassle to keep taking masks on and off whenever I wanted to walk into a shop or restaurant or grab a coffee.

I asked people why this was the case, because when I'd been in CDMX and Puebla in June, masking was by and large over. They said it was because state health authorities in Oaxaca continued to advocate mandatory masking, although I was also told that rule might be changing soon.

I didn't really mind the masking rules to be honest, and I complied with whatever people asked of me, but it was absolutely theater and as far as I'm concerned served absolutely no practical purpose other than making it look like people were doing something.

In Guerrero, masking is still mandatory in Hospitals, Pharmacies, etc. Everyplace else voluntary/determined by establishment.
In Acapulco in September, there were still many wearing masks, all over.