I get them too.
Apparently it was caused by some Windows update some time ago.

Some people find that using Vulkan launcher clears up their FPS.

But for me, that doesn't work. What works for me is to open the menu by pressing "Escape" each time the framerate drops.
Then I enable v-sync > apply > disable v-sync > apply > enable vysnc > apply...
Repeat for a while and the framerate should clear up within 8 seconds.
However, every two nights or so the framerate will drop drastically and you have to open the menu and repeat the process.

I heard you can rollback the update, if you know how.

Most solve the problem with Vulkan launch, if it doesn't work for you I'd recommend rolling back the windows update. There are multiple guides for rolling back windows updates online. I've personally never heard of the v-sync method described above but I guess you could give that a try as well. Doesn't sound convenient though, you might want to look for a permanent solution instead.

If Vulkan fixes your problem, you can go to your steam library in the properties of the game and add `-vulkan` in the laucnh options of the game. This is just for convenience so you won't have to manually pick Vulkan every time you start the game through the library since it starts in DX11 by default.