choppy ui lagging I tried everything! help

Hello, i recently bought a macbook pro 13 2015 listed as no wifi/bluetooth and it was cheap i knew it from beginning that the io board was faulty but it doesn’t.

I opened it up i clean fans/dust, repaste it and i just saw that the pin connector of io board that goes to motherboard was off, when i take it in io board working normally wifi/bluetooth, performance was the same.

i have ui lag on mac os scrolling in pages, open apps its not smooth like others and my temperatures are really low when i browse to youtube cpu temperature is just like to max 70 celsius.

i have tried everything from smc,pram reset to test it without battery, deleting com.apple.windowserver.plist and updating to monterey that it seems to be a little bit faster but i downgraded to mojave.

the guy i bought it from he have performed a battery change but when i opened it up i think battery its not original/oem and maybe this is the problem that causing slow perfomance, when i performed apple diagnostics said that battery needs service and it has now like 50 cycles something like this.

i dont know i gave up i dont have any other suggestion to do.