I'm getting closer with this but still running into some issues. I've managed to create a remote repo and connect that to my local repo outside the context of DM. DM recognizes the local repo just fine and I can use it for local commits. But when I try to push I get this:

In bash, I can push that same commit with no issues:

If I try to pull inside DM I get a similar error:

Note that the height of the error response is cutting off the full message.
I must be missing something related to how DM can read/access my public key but not sure where to look for more clues. This is the dialog I get from DM overlaid on my bash shell when I click the Remote button. Perhaps using ssh vs https?

Well, that's an error coming from Git. Make sure you can push with that account using your normal git client or command line. Pretty sure that also won't work - looks like you have read-only access to Git in this case.
FWIW, you can mix and match Git clients. Most places in the UI let you Open in Terminal (Tab, Context Menu, Tools etc.) and from there you can use command line with Git as needed as well.
+++ Rick ---
On second thought:
Your Git Repo is accessed through the permissions that are set up in the Git command in Windows. The only thing I can think of is that you're using Git through Bash which is not using the raw Windows environment, but Windows Subsystem for Linux or the Bash Shell (also some Linux shell). IOW, you're not using the Windows installed version of Git which is likely configured separately and which is what any desktop client will be using (ie. Documentation Monster, Markdown Monster etc.).
FWIW, you don't need Bash to access Git - you can use Command or PowerShell and that's how at the very least you can debug and see if you get the same behavior and you can debug from there. Or use a visual Git Client. Or if you use WSL I think there's a shared version of Git that uses the Windows install of it.
FWIW, you can mix and match Git clients. Most places in the UI let you Open in Terminal (Tab, Context Menu, Tools etc.) and from there you can use command line with Git as needed as well.
IAC make sure you use the Windows version of Git and that that version of Git has the required credentials set up for your Repo (ie. Windows Credential Store most likely).
FWIW setting that up is likely going to be easier via some of the full Git Client like GitHub Desktop, GitKraken, SourceTree, SmartGit etc.
Thanks.
Yeah, I know I can use other shells. I'm using the bash shell that comes with the git Windows distro. Been doin git stuff this way for years. I run Pageant at startup and add my preferred identity. In bash, I get the PID and add my identity there. My shell is up and running all the time so it's a one-time thing.
What I was trying to show in my screenshots is that I can push and pull for this repo in bash; the failure is happening with the git integration in DM. But I think you're on to something as far as the available identities loaded in that context. If DM is effectively using ssh in the same context as PS then I have another clue.

I was able to start the ssh-agent service via PS and add my identity.


But DM is still not happy.
You said I can invoke a shell directly from DM? That option isn't jumping out and biting me...
FWIW I do use a GUI git client. Years ago when I first started with git I installed Sourcetree but I haven't used that in ages. The shell works fine for me. I am successfully using some of the integrated git plugins for VS Code but otherwise no dedicated GUI client.
Found the Open Folder in Terminal option. Will see what I can see.
Running git commands from a terminal invoked from inside DM gives the same fatal results. Personally I can live with pushing to the remote from my standard bash shell but once I get others using this, particularly the non-engineer, I'll have to figure out why it's not finding what it needs.
It's not finding what it needs because you have Git setup in your Bash shell which is a separate Linux sub system, not in Windows. These are two different things and they have separate Git installs and configurations.
This is why I'd recommend that you don't use the Bash shell, but either use Command or Powershell, or if you need to use Bash for Linux commands, use Windows Subsystem for Linux which shares the Windows Git install and credential store and in general has better interop between the Linux and Windows environment (ie. you can run Windows executables out of the Linux shell, you have access to the local file system, registry etc.).
That way it'll work with any tool that you use to access Git. Any external tool you use will also use the Windows store.
You can also keep doing what you are doing, but you have to explicitly set up the remote again either from Git on command line or from within DM or other tool.

I haven't used that in a loong time because all of my repos tend to be set up in SmartGit or TortoiseGit - but I suspect it should work 😄
+++ Rick ---
I've got my system configured to use ssh by default, not https.
When I attempt to Attach to Remote Repository using https, I get

Same thing if I use the ssh format.
I'm going to install Github Desktop and see if that will allow me to figure this out.
I installed Github Desktop. It made me re-authenticate as part of the install which I did using a combination of a browser tab and 2FA. Once I did that I was able to connect my local repo to my remote:

However, when I pulled I got this dialog:

I think the next step might be to gen a new ssh key but like you I haven't had to mess with this in ages
I went into the advanced options in Github Desktop and enabled a setting to :Use system OpenSSH (recommended)

Once I did that I was able to pull and push from GHD. Still no joy directly from DM. I think I'll have to go find the hoops to jump through for creating a new ssh key pair next.
Figured it out!
For any lurkers, I had to change the remote protocol used from ssh to https, and then initiate a git action via DM. In this case, I did a pull. I was prompted to authenticate and after that DM was properly connected to my remote repo.
The first step is to change the remote URL in (presumably) any shell. I happen to use Git Bash in Windows but I'm sure PS or CMD will work just as well.
git remote set-url origin https://github.com/<your path>/<your repo name>.git
Then in DM, open the Git form and do a Pull

After that, follow the prompts to authenticate.
You can use your SSH key with the Windows Git credentials too, but you have to set it up outside of Documentation Monster as that only allows hooking up the remote via Http.
That said, once configured any Windows based Git tool will use the cached credentials. I never use the remote hookup (I probably should) because I always use external tools to create and hook up my repositories to remotes (SmartGit and TortoiseGit for me) and I also use Http because it's a heck of lot easier to deal with than SSH keys especially if you use Git integration in many tools and you have to configure clients. Http uses oAuth with GitHub so it automatically does the right thing.
+++ Rick ---