Here is my thoughts:
Now i understand why you get 10fps! You have a HUGE 65" 4k tv and using an iGPU!
You NEED a good GPU to get the best of it and of course your experience will get a huge jump.
First PSU: No way a 550w and undervolt a 3080. Just no.
You need at least a 750W/850W GOLD PSU. I would recommend a 1000w.
My advice is a CORSAIR HX1000 or a cheaper one if you prefer XPG CORE REACTOR 850W Gold.
Psu is something that will last you at least 10+ years. Specially CORSAIR. Never save money on a PSU.
GPU: Since you are thinking about going for a big card. Forget this iCHiLL
Go for a ASUS TUF 3080 or ASUS ROG STRIX 3080.
EVGA 3080 FTW3 or (the one i have which is HUGE but have one of the best cooling around)
MSI SUPRIM X 3080 (its 40cm long though)
Those cards tend to get VERY HOT while using MSFS, you need a good cooling. I usually play on 2k and it uses 95% of its power. So forget about undervolting.
Also those offers warranty for 3 years, its important since most of them only gives 1 year like gigabyte and probably that one you mentioned.