I don't have enough space on my MacBook (running on Catalina 10.15.7) and I found 6GB folder named Updates which is located in Library - my question is: Can I safely delete that folder ? I think that folder is filled by old updates from Catalina old version so.. I don't know if is it safe to delete everything which is in folder or not.
I would say no. I have people move other files to an external drive if they are not sure their backup is solid. If you have a solid backup, you can just delete files.
Once you have 10 GB free run the updates until you are clear of this.
sudo softwareupdate -aiR
Quit all apps before or right after you start this (except terminal app of course).