A very simple but potentially quite a big time saving tip this time.
Typically, when you are developing for Windows Mixed Reality, you spend a lot of time in the Unity editor getting things just right. Unity and Mixed Reality integration is awesome - you can just hit play and your scene will show directly in your head set.
But sometimes, that is just not what you want. If you are fiddling with a tiny bit of interaction or animation code (and we all knows that can take a lot of time in Unity) you often just want to hit play, observe the results in the Game window, maybe move a bit around with the WASD keys or using an Xbox Controller. In that workflow, the necessity of putting on a Mixed Reality device - and taking it off again - for every little iteration can be a cumbersome process.
There are two solutions for this: first, unplug your device if you don't need it. Duh. But if you use big desktop development box or this means reaching out to the back of the device. For laptops and desktop boxes both, you will need to fiddle with plugs, which in time might wear out or damage the plugs and/or the plug sockets of your PC. I am unfortunately speaking from experience here.
So what to use? Good ol'e device manager. Simply type "Device manager" in your start menu
You will find a node "Mixed Reality Devices". Find yours (I have a Samsung Odyssey indeed). Simply right-click
Hit "Disable device", click "Yes" on the rather ominous following warning, and your headset is now an expensive paperweight, no longer paying attention to what Unity does. You can now use Unity Play mode the 'old' way.
If you are done finicking in Unity, you can simply enable the device again using the Device Manager, and your awesome headset wakes up again.