Wi-Fi connection issues/lag after OS update

Hello,

I have a 2017 MacBook Air that was running High Sierra until Saturday (August, 28) when I decided to update to Big Sur. The update caused a load of issues with my Air, including major lag, app issues, and constant Wi-Fi drops. I then downgraded to Catalina, but these issues have continued. It seems to work as normal when I'm connected to my 2.4G network, but as soon as it connects to my 5G network the computer lags, pages do not load, apps don't open properly, and it's always dropping and reconnecting every few minutes. What can I do to fix this issue? I've tried EVERYTHING: safe mode, resetting Wi-Fi settings, resetting my NVRAM. I was exclusively using my 5G network before my OS update, and I would like to be able to use that network again without issue.