I live in Brazil and its pretty hot almost all year around here as well.
You need probably a better cooling inside your gabinet. A GPU while running MSFS will get to around 60-70 celsius. No way to get less than that. I have 8 fans inside my gabinet and still leave the glass door open while playing MSFS. My card run around 65 Celsius and if noise isnt a problem you can power up the GPU fans.
One thing is if you are going for an upgrade, its better to save for a while an get good hardware instead of buying cheap PSU/GPU. You can get a CORSAIR 750W Gold for cheap and will do the job.
About the GPU: 3080 is a hungry in power and much more powerfull than Radeon 6700xt. A good one to compair is a 6800xt which tends to get VERY HOT. 3080 uses GDDR6x which is much more powerfull and get way more hot.
Since you are playing on 4k i cant see you using anything other than a 3080.
And the way ASUS,EVGA and MSI build they top tier cards for gamers is exclusivelly to get the most of them. They use the best cooling systems, the best thermal and also the quality of overall materials are top noch compared to smaller cards and other brands. That makes a huge difference and thats why they cost more.
3080 in small size are nonexistent because of all that i mentioned. And i had experiences with other brands already. Coolers tend to make a lot of noise and not working after a while, memory starts to get hotter due bad thermal pads and construction.
Read about the EVGA cooling system called: iCX3 and MSI Tri Frozr 2S.
the mechanism on them etc… They are built to run fast all the time if you need them.
You can also control speed and they are not noisy as most of the coolers around.
Those cards are built to run at hot temperatures so i usually leave on automatic cooling.
One last thing. Getting a powerfull card and undervolting it, there is no point in my opinion.
Its the same if you get a powerfull car with 400hp and make it with 100hp.