I typically learn by reverse engineering what I need to make things work. I google the file in question and find someone that will tear the file apart and will explain what each line means and how to edit. Or I open the file in Notepad++ and find a typo or incorrect formating that I can correct.
Authorized keysOptional, paste ssh key for ssh console access
I did try to ssh into OPNsense on my Windows 11 pro. Thought it was going to work until it rejected the password.
ssh root@<your firewallIP>
ssh -i .\.ssh\keyfile <username created above>@<your firewallIP>
You did enable password authentication in System > Settings > Administration?
You are aware of the extensive documentation?https://docs.opnsense.org/manual/how-tos/user-local.html