Which game can two people play online on the Xbox with one device, does anyone have any idea?
It is becoming increasingly rare but a very current title is e.g. Dirt 5
The main problem will be that you will need "XBOX Live Gold" or "Ultimate" to play online. It's similar to PS because it simply says "PS +"… And otherwise there are hardly any games that allow that.
As far as I know, almost the entire COD (Call of Duty) series can do that. Just like Dirt 5 and ARK SURVIAL EVOLVED - to name a few examples.
Otherwise there's still World War Z or Dead by Daylight I think… Otherwise there are classics like Minecraft and a few other games from Game Pass!
This works with many Nintendo Switch games. Xbox is the wrong console for it!