I was using Blender version 2.90.1 yesterday (11 Nov 2020) and it was working fine. Last night a windows update was forced on me when I shut down the computer . Today when I opened version 2.90.1 it was extremely sluggish. It is now difficult just to drag the default cube from one side of the screen to the other in the default layout mode. It just jerks across the screen lagging the mouse cursor. Switching modes (i.e. object > edit > scalp) is also slow and typically takes 3 > 5 seconds to respond. Going back from scalp to object mode can take around 20 seconds at times. Before the windows update, switching modes was more or less instantaneous (< 1 second).
I switched to Version 2.83.4 which is still installed on my computer and it seems to work fine without any lag.
The only thing I notice about both versions is that the UI looks slightly different for both. The grid lines appear to be a little bit thicker and the grid is more prominent (possibly just the extra line thickness).
I uninstalled Version 2.90.1 and installed 2.90.0. It performed just as badly as 2.90.1
I checked the video drivers. They appear to be up to date. Rendering time on the default cube in Eevee is about the same (10 seconds) for both version 2.83.4 and 2.90.1. I also checked that all the installed user add-ons were the same for each version. I completely removed a few user add-ons that I am not currently using. I tried another graphics program (Krita 4.3.0). It seems to work fine.
My computer is a Toshiba Satellite Laptop 64 Bit with Intel 2.40 GHz processor, 16.GB ram and dual monitors. Switching to a single monitor made no difference. The operating system is Windows 10 Home edition Version 1909. Windows won’t allow me to roll back the update claiming that it is more than 10 days old which it obviously isn’t.
At the moment I have run out of things to try. I was wondering if any body else is having similar experiences or can offer any suggestions.