Those db files are backups of your main plex database. You better don’t delete these.
You may empty out the ‘Updates’ folder.
The rest of the folders is maintained by the Plex server butler. Make sure to activate check boxes #3 and #4 https://support.plex.tv/articles/201553286-scheduled-tasks/
The rest of the folders cannot be “safely” deleted.
Get a larger SSD
or
a second SSD and move the data folder over to this new drive: Moving Metadata on Windows
