Steam does not support multiple players using one Steam account simultaneously - games associated with a Steam account are licensed for the sole use of the account holder.
If multiple users attempt to log in and play simultaneously with one Steam account, the user who logged in first will eventually receive an "Invalid Steam UserID Ticket" error message and be forced to log back in to continue playing (if the first user logs back in, the second user will receive this error message).
I have to use this shit for work. If you don't set your cookies to auto delete it is basically impossible to go through the Microsoft SSO after around a week. Just use a decent password manager if you can and press enter 4 or five times.
It would be that easy, if not for "please approve login on your microsoft authenticator app" step which means i also have to pull out my phone, unlock it, find the stupid app and then type in the code