I hoped #191 would fix it, but I built it and it still freezes, not sure if the failure point is the same.

It appears that the native windows crypto backend wincng doesn't seem to support elliptic curves at all.

I have a branch where I enabled the openssl build for windows too, would be great if you could try it out.

You can build it cross-compiling from linux unsing mingw, or natively on windows using MSVC, but you need a valid perl installation (see Strawberry Perl for example), and NASM (I also had to manually add to the installation dir as part of the PATH env variable, but YMMV).

This blog post says that it's a limitation of libssh2, it supposedly doesn't implement ecdsa with wincng even though wincng supports it (the microsoft documentation says that it's supported too).
Edit: EdDSA and ECDSA are different, my bad.

After building the branch, the issue is fixed if the credentials are correct, but if they're not (if one forgets to enter their passphrase), the editor still freezes in the same way.

In the API docs for libgit2, the description for git_credential_acquire_cb says

Note that most authentication details are your responsibility - this callback will be called until the authentication succeeds, or you report an error. As such, it's easy to get in a loop if you fail to stop providing the same incorrect credentials.

As far as I can tell this callback is involved only with ssh auth. It seems gitlib2 expects this callback to return an error for incorrect credentials, which seems like a weird design decision to me. Even when authentication works, the blocking loop makes the editor freeze for around 4 seconds.