Some of my testing implies that using "remote.SSH.useLocalServer": true overrides/overwrites/disables/ignores my global SSH_ASKPASS mechanism on Windows 10. It works fine without the local server. I have tested a bunch of clients, including Win32-OpenSSH (OpenSSH_for_Windows_8.1p1, LibreSSL 2.9.2), Git for Windows ssh.exe (OpenSSH_8.5p1, OpenSSL 1.1.1j 16 Feb 2021), and Cygwin's ssh.exes (OpenSSH_8.5p1, OpenSSL 1.1.1f 31 Mar 2020).

I don't have a major issue with that, but should documentation be coming in the future (compare #4492), this might also be considered.