vladimírfrompraha wrote:
Except it is not how it worked up until now. Deleted files were shown as free space immediately.
It's been many years since the system behaved that way. You may not have noticed it until recently.
I made a fresh OS install, restored backup and it works again like it did. After the update suddenly even browsing was filling up free space. I did not notice it at first but in three days it had filled 250GB of free storage.
The most likely explanation is some kind of 3rd party app that isn't compatible. But remember that's just the "most likely". There are dozens of possible causes.
When you do an OS install and then restore from backup, you're essentially restoring the system to exactly the way it was before. That might delete "system data", but only as a side effect. Your restore process also restored whatever had caused the problem in the first place.
What you have to do instead is erase the hard drive, reinstall the operating system, and then don't restore from backup. You can restore your user accounts and user files. Just don't restore any software, apps, system settings, or "other files". Then, you can manually reinstall only the apps that you absolutely need - that you can't live without.
Even if you do that, there is always a possibility of some system problem causing that. It's just that Apple causes are relatively rare. They do happen, but it's relatively rare.