Insignia 4k firetv help

[huhi]

Hello, recently my old tv broke and I needed to buy a new one and I got one on black Friday. I got an insignia 55" 4k fire tv from BestBuy. I usest to play Forza on my old tv no problem and now I can't even seem to run it. That is not the reason why I am here, I am trying to change the resolution of the HDMI ports from 4k to 1080p to see if it boosts the fps. I have a good enough HDMI cable to where I know it's not that. I have a 3080, 5800x in my PC so I know my PC can run 4k pretty easily but I can't seem to get the fps above 15. I have changed the Hz to the max which is 60. when it was at 30 I could not get above 7 fps so that increased it but not to where it should be. I have tried many many times to hold the up button and the rewind button for a bunch of seconds so that I can get the secret resolution menu up. I then wait till it says you are currently on 1080p 60Hz and choose it. when I go back and check the info it stays at 4k. what else can I do???