Same problem here, with my wife running Shotcut on Windows 11, suddenly on a rainy Friday afternoon complaining about performance issues and not being able to work with Shotcut, without any (automatic Windows 11 updates aside) software/hardware changes since the last time she was working with Shotcut without issues.
It was thanks to this post in another thread that I was lead down the path to Grammarly:
It took me several hours to figure this thing out, and I am a software developer (working on Ubuntu btw ;)). I asked my wife if she installed this Grammarly cr*p herself, but she could not recall. Maybe this malware was shipped with some automatic Windows update. One can only guess how many Windows users stumble upon this same issue not knowing how to fix it. We tried everything, from optimizing settings in Shotcut, CPU/RAM profiling, to rolling back Windows updates and Shotcut versions (including registry settings) to no avail.
Maybe it is worth mentioning this issue with Shotcut + Grammarly + Windows 11 in some troubleshooting guide, on the website perhaps? I could not find one.