I messed up the version number in the folder link name. It's version 20.03.02, the newest version, in the hidrive and mega links.
If you download the newest version you don't need the update files. The "update files" are to upgrade from version 20.02.08 to 20.03.02.
I made a video about using update files and moving save files here:
1) thanks for the reply
thats what I wanted to try to do first - but then decided to wait a bit first
2) copied the files like in your video but itch wanted to still update the game - so to avoid this mess and further trouble with the itch-updater - I backuped the saves and deleted the game to re-install it
3) deletion worked but re-install doesn't work either
3a) for the HiDrive folder - "An error occured during installation No manager for installer unknown"
3b) for the MEGA folder - "An error occured during installation runtime error: slice bounds out of range"