Is anyone testing new titles at Microsoft?

Early access or insider program? the game is being released on May 2020, you should try to contact the developer'ssupport:

https://inxile.zendesk.com/hc/en-us

Hello RudolfDvoracek,

Thank you for posting on the Xbox forums. We understand that you are unable to launch Wasteland 3 on you Windows 10 computer.
Did you pre-order the game? Wasteland 3 is not available to play at the moment. It does not get released until
May 18, 2020. Be sure to let us know the results!

Did you preorder the game or have game pass? You can install some parts of games before they come out and when the game is close to coming out the full game will download if you have the game preordered or game pass.

Hey Rudolf

Thank you for taking the time to reply to this thread.

As stated by Xbox Forums Ambassadors
DustyStraws&
k1Helix z, certain games that have been pre-ordered will occasionally let you install the game prior to release. This acts as a sort of place holder for the game itself.

Upon a closer date to the release of the title, an update is usually passed out that carries the larger chuck of the game, so that you can play the game upon the actual release date.

I hope this was able to clear up any confusion or turmoil this might have caused.

As you have already been provided with the best info on this matter, and in order to prevent further repetitive answers, we will now be locking this thread.

If you have any other questions or concerns that differ from this matter, please, feel free to create a new thread and we will cater to you there.

Thank you for being part of the Xbox Family and we wish you a wonderful day.

I looked it up on my xbox app and I see what you mean, you downloaded a preload of the game, if you check the game's page on the app (the screenshot you provided) below is the release date set as May 15 2020 and the game's size is 10MB which is impossible.

You will have to wait until May to play the full game, it is still under development