Can you play on two devices at the same time with a Minecraft account?

Is that possible?

Of course not.

The Java edition? Yes, but not on the same server at the same time. If you play on different servers or even single player, this is no problem

At Bedrock Yes, i.e. With the same Xbox account once as a host and as a client (who joins), the device does not matter - whether Xbox One, Windows 10 PC, Android, Ios, Amazon, or Nintendo Switch goes both locally via LAN / Wi-Fi, or online. (When online, the process does not work with 2 Xbox One consoles. You can only log in on one.)

Yes you can.

You can install it as often as you want. Even on several devices at the same time. You can only play on one device. You can download and install MC as often as you want, on as many devices as you want