Usually you don't accidentally open a git repo and set up a ssh key and push your own credentials to a foreign repo. Usually that involes reading a manual. If those tutorial don't cover keys, then the tutorials need to be improved. imo

Generally if you want to combine full encryption with version control, your best bet would be instead to not use something like Forgejo, and instead do something like init a local git repo, commit like usual, then set up scripting that will tar.gz archive the entire repo, PGP encrypt the archive, and then upload that to a cloud provider's file storage. That way, it's got privacy (the archive is encrypted), it's got version control (once decrypted and decompressed it goes back to being a folder with a git repo in it), and it's backed up (via cloud file storage provider).