Big Picture includes an on-screen keyboard overlay that you can toggle with a shortcut (by default it's the controller "home" button and "select", iirc).

The first time you try to unlock the PC this way, Steam will prompt for elevated permissions to be able to do so.

You can of course also set up the user to be automatically logged in.

In my experience it's best to have Steam launch via the Task Scheduler with elevated permissions so that you can approve UAC requests, etc.

However, yes it's worth having a keyboard connected (even if it's just one of those tiny wireless touchpad+keyboard combos) in case things go wrong.

Microsoft used to sell a keyboard attachment that would go on the bottom of an xbox controller. I dunno why they stopped selling them, they work great for things like this.

If this really mattered, you could use a Logitech Brio to sign you in with Windows Hello

It’s a gaming PC, why do you use a password? Is someone going to break into your house and steal your PC on to be thwarted by your password?