Honestly, there is no reason the family PC should be windows. Windows has become an entirely inferior product for everything except some specialist software which you can not run through wine. But for that just use a windows VM

Yeah precice phrasing ia hard sometime. I was refering to delete/modify of files as “changes to the fs”. Not sure how changing the actuall fs would be relevant to the backup question.

OP needs a restricted shell that can take backup data and write it to disk but not be able to modify anything that is already there. Nano and rsync can both do that.

Nano and rsync are 100% designed to modify the filesystem. But yes the idea is correct.

Same with got over ssh, you restrict the connection to the got shell that can only do the things you want.