It was a month ago and I didn't note down all my attempts. It went something like:
Pushes were not working. I re-entered my password a few times, checked other config settings a few times before Googling the Git error message, which led me to find that GitHub's security policy was changing.
I tried an SSH login (fail), switched to trying locally generated SSH keys.
Used PuTTY's "puttygen.exe" to make an SSH key. Did that, then found it was a newer format that Tortoise could not handle. Used TortoiseGit's copy of "puttygen.exe". Did this a few times as GitHub wouldn't accept the format that my key was in.
Gave up on GUI key generation, tried command-line and failed a few more times.
I think I looked at personal access tokens at some point.
Went back to GUI SSH file creation, and managed to upload my puttygen SSH key by copy/pasting from part of the dialog box that I hadn't tried before.
Used GitHub's "git@github.com:<username>/repo" syntax to get a fresh clone of my repo. Finally I realised that I needed to use the github URL syntax combined with "Load Putty Key" ticked and pointing to my private key
I'm still not sure if it's the right way or the best way, but it worked, so I stopped looking.
I don't think I can recommend anyone use PuTTY on Windows anymore, partly because of issues like this. It might be that TortoiseGit is old, but ssh.exe should be available on Windows 10 now.
Pushes were not working. I re-entered my password a few times, checked other config settings a few times before Googling the Git error message, which led me to find that GitHub's security policy was changing.
I tried an SSH login (fail), switched to trying locally generated SSH keys.
Used PuTTY's "puttygen.exe" to make an SSH key. Did that, then found it was a newer format that Tortoise could not handle. Used TortoiseGit's copy of "puttygen.exe". Did this a few times as GitHub wouldn't accept the format that my key was in.
Gave up on GUI key generation, tried command-line and failed a few more times.
I think I looked at personal access tokens at some point.
Went back to GUI SSH file creation, and managed to upload my puttygen SSH key by copy/pasting from part of the dialog box that I hadn't tried before.
Used GitHub's "git@github.com:<username>/repo" syntax to get a fresh clone of my repo. Finally I realised that I needed to use the github URL syntax combined with "Load Putty Key" ticked and pointing to my private key
I'm still not sure if it's the right way or the best way, but it worked, so I stopped looking.