When upgrading from 2018 to 2020 Unity, my project suddenly goes from running fine to like 5fps?

My projects were running fine in unity 2018, but as soon as I upgraded (this is along multiple different projects, including a new one I made in 2020), my fps just became horrible. The stats says that I’m getting 40-50, which is not bad for now, but the actual view can’t be more that 2-5 fps. It is impossible to test my project like this. Any ideas? I have tried vsync on and off, and different resolutions, and just about everything I can think of, but nothing is any better. Any ideas?

It’s actually very laggy in the editor as well. I am very confused, though, because it was perfectly fine in unity 2018… were there any huge differences in that respect? Are macs suddenly super unoptimized in 2020?

Do I need to wait for the Global Illumination Preprocessing to finish?

You are likely running into the issue discussed here: 2021.1.22 + 2020.3.19 huge performance issues affecting mac

You can temporarily downgrade to a slightly older 2020.3 release in order to avoid it while we get a fix out.