I had a 1990 Nissan Sentra (bought brand new) and when it was still relatively new and under warranty, I felt the AC wasn’t as cold as it should be. I took it back to the dealer and they corrected the issue. I remember them telling me “we just charged it up a little.” I didn’t know what that really meant but I see someone above mentioned charging it, so that might be relevant.
I had a 2008 Honda Civic (also bought brand new) and I put a lot of mileage on it, with over 500 miles on it per week. At one point when it was getting up there in mileage, the AC was not working that well. I had a friend who is an HVAC mechanic (on residential and industrial, not on cars) come take a look. He got a can of freon which you can get at any auto parts store. He tried to put the freon into the car’s AC (where ever it goes). He told me if the AC doesn’t need freon, it won’t accept it. It didn’t need freon so it never came out of the can. Obviously there was something else wrong with it. Luckily the hot weather had already passed that year and the following Spring, the car went for good with over 210 miles on it. Never had a major problem which is what made me a “Honda Convert” for life. Anyway, if you get the can of freon and that’s not the problem, not much lost out of your pocket other than $20.
You can also bring it to the dealer for diagnosis for not a lot of money. It will tell you definitively what the issue is.