Yeah, you have two options, as the server owner:

1. You can enter a user’s email from the Plex UI to invite a user to your library. The user then gets an email asking them to sign up if they don’t already have an account.

2. You can generate/send a link to join, any way you choose.

Once signed up, the user can accept the library invitation, then they login to the TV or other device. The code is used for the TV login process, like on other streaming platforms. But yeah, you could do an account-less version of this for Jellyfin, which I think laypeople would like.