Mac OS Account on an External Disk?

I need a Mac that is often offline for confidentiality. Is it possible to store an Admin or General User account on an external disk which I could only login to when plugged in? In my instance it's not as simple as just storing documents/apps/libraries on an external disk; I need the dynamics of an entire account.

A variation of this I'm opposed to is logging in through a local network account server I make and then unplugging the disk when not in use, problem being that it opens more vulnerability's than logging into an account on a thunderbolt connected disk; so one might think this isn't an unheard of solution.

This would be far less of a hassle than having to manage security precaution and system updates on another Mac.

You can also install a complete system on an external ssd and when you want use it, you boot your Mac on this external ssd and all users and system informations will be only inside the external disk.

I would copy the entire ~userid to the external disk. Then, using a different account with admin privileges, delete the original and change the default home directory to the new one. After which that user can’t log in unless the external disk is mounted.

Is there any equivalent command for usermod? for more info.