Can you explain in a bit more detail what you are trying to do and what does (not) happen? Include the version of Lightroom and the version of your OS. And perhaps include a screenshot? Don't attach it, embed it, by using this button:
Problem has started since I upgraded to the newest LR version and lost all of my previous work that was kept in the Collections section.
I started from zero images on the newest update and couldn't figure out how to get all date back. I tried to load through the backup folder but didn't worked.
Now I wanted to go back just to a few images that I shoot in many years ago, like 2017 (don't know what version of LR was used)...
I wanted to import the new RAW images to edit again and during the upload it popped out as "could not copy a file to the destination folder because it is not writable or there is not enough free space".
If I upload new RAW (never edited images), - there is no problem and it shouldn't be space issue here.
If you lost previous work, then you should solve that problem, not create a new catalog. Losing work normally just means that Lightroom lost the connection to its catalog, and created a brand new one. Search your Pictures folder for the old catalog, and when you found it, double click that catalog file to launch Lightroom with it.
Your second problem is probably unrelated. As the error dialog says, you instructed Lightroom to copy the imported images to a place that was either out of free space, or Lightroom has no permissions to write to it. Most likely the latter. So check what you selected as destination.