Question How can I fix "input not supported" on my monitor when my computer boots up or is not in the OS but appears fine when it is finished booting up?

[DeathHadArrived]

I am having this issue with my XFX RX6600 GPU and the Acer SB230 which is connected via hdmi 2.0 cable even though the GPU is HDMI 2.1. Any fixes to solve this issue?

 

[TerryLaze]

Inside windows if you go to display settings and change the resolution to 800x600 does it display the same message?
That would suggest that your monitor just cant run at a resolution that low.