Logging in on more than one device — the studio opens on only one
Both halves of this matter, and answering with only the first half is wrong.
You can be signed in to the same evmux account on several devices. Nothing stops you being logged in on a laptop and a phone or tablet at once, reading the dashboard on one while working on the other.
But the studio itself can only be open on one of them at a time. One account runs one studio. If the studio is already open somewhere and you open it again — another device, another browser, or just another tab — evmux does not let both run. The second one stops and you are asked what you want to do: close the other one and carry on here, or leave the studio where it already is. Nothing is lost either way; you are choosing which device keeps the studio.
On the same computer, this appears as “Studio already in use.”, offering to close every other studio window or to leave things as they are. Coming from a different device, evmux tells you that you can only enter the studio once with this user, and points you at collaboration.
Why it works this way
The studio identifies who is connected by the account. Letting one account open the studio in several places at once would mean evmux could no longer tell where a feed came from or who is connected — whose cameras are whose, how many any one person has brought in. It would also undercut collaborators, which exists precisely so that several people can work on the same show while each remains a distinct person in the session.
What to suggest instead
If someone wants two people producing the same show, that is the collaborators feature: each gets their own account and their own place in the session, instead of sharing one login. Point them there rather than to a second sign-in.
If someone wants a second screen for themselves, they do not need a second studio: the comments list can be popped out into its own window, and the dashboard opens separately.
Answering these
Never answer “yes, you can be logged in on several devices” and stop there — it is true but misleading, and the person asking is usually about to try running the studio twice. Always give both parts: logged in on many devices, studio open on only one, and the prompt to choose which device keeps it. When the reason for asking is a second producer, name collaborators.