Game will not start - PC NOT A BUG

EDIT: the problem also presents with different, non Klei games on Steam. So obviously, this is not a bug Klei needs to fix but something with the Steam client. I will keep this up for clarity's sake but feel free to delete it.

I try to start up the game on Steam. The window "preparing to launch" shows shortly, then disappears. After another second or two, the steam button changes back from "exit" to "play". The miniature that is supposed to show up in the taskbar at the bottom of my screen never shows, not even the outline. 

I have tried the following:

- verified files (also several times after the other attempts. Assume I did this for every change)

- restarted pc

- uninstalled and reinstalled ONI

- start without DLC. ! This works fine - at least up to the main menu, I have not started a new game because that's not what this problem is about.

- reinstall DLC, same problem

I searched the forum for an answer. I found a similar sounding, recent one, but it is  on Mac: 

There is a solution proposed in this post:

1. Browse the Local Files (right-click ONI -> Properties -> Local Files -> Browse Local Files)
2. Go into the OxygenNotIncluded_Data folder and delete StreamingAssets
3. Verify Integrity of Game Files (right-click ONI -> Properties -> Local Files -> Verify Integrity of Game Files)

I have done exactly this, especially since I was included in Alpha testing. The details are: 868 files not validated, automatic download for update, size: 414.3 MB

I retried, but the game will not start, same as before. I set back the streaming Assets for the moment as I wish to change as little as possible. 

I am at a loss. I played just yesterday on my other PC, which is older and less powerful, and I do not recall seeing any updates queued. 

Edit to add: The wording of the Steam buttons might be slightly different in reality. I translated from Dutch, as that is my Steam language setting.