I've only just uploaded to Big Sur and updated Indesign to 16.2.1.
I am having terrible trouble with the speed of Indesign now and I'm constantly getting a spinning beach ball for the smallest tasks, such as dragging a copy of an image.
I have 16gb of RAM on a MacBook Pro (15-inch, 2017) and haven't had issues in the past.
I have a MacBook Pro (15 inch, 2016) with 16Gb of RAM, Big Sur and InDesign 16.2.1. I have none of the problems you're experiencing.
To start with, I would restore your InDesign preferences and caches:
I'd also make sure you've updated to Big Sur 11.3.1.
If that doesn't work, you might uninstall InDesign and reinstall.
I just followed all those steps but no joy.
I am using Big Sur 11.3.1 but I'll uninstall and reinstall and see how I go.
Thanks again 🙂
I'm linking to some files on a server, I think this is the issue.
All my files are stored locally. Not having access to a server, I wouldn't have tbought of that. That could do it!