Why is my monitor blurry after I switched back to 1080p

hii,
I got a 4k monitor and wanted to mess around so I got windows to run in 4k. I decided that I would only use it for games and switched back to 1080p and know my screen still has that weird fuzzy thing 4k gets. It now looks like trash, how do I fix this please

Thanks!

I didn't find the right solution from the Internet.

References: https://www.cnet.com/forums/discussions/...-back-to-1080p/


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