How to change the system folders (Pictures, Movies etc)

It used to be possible (before Big Sur I think) to rename and remap the system folders (Pictures, Movies etc). What I am trying to do is move the folders to Dropbox like this:

sudo mv ~/Documents ~/Documents_old

ln -s ~/Dropbox/Pictures ~/Pictures

When I do that I get the following message:

mv: rename /Users/neilthompson/Pictures to /Users/neilthompson/Pictures_old: Operation not permitted

I know that it used to be possible because I have been doing it since 2014 but just moved to a brand new machine and now it doesn't work.

Anyone know of a workaround?

You need to give full disk access to Terminal to make it work - those permissions seem to have changed in Big Sur. Go System Preferences -> Security & Privacy -> Privacy and grant the permission to Terminal. Even files that look like you have full control over them (based on unix permissions) can be impacted.