[2020] Fix your launcher.

The launcher has certainly had its issues, but I have never seen or heard of that "insert the disk" problem before.

Let's skip that step and do a clean install with new launcher files.

- exit the Steam app entirely

Delete the following folders if still present:

- C:/users//AppData/Local/Programs/Paradox Interactive/
- C:/users//AppData/Local/Paradox Interactive/
- C:/users//AppData/Roaming/Paradox Interactive/launcher-v2/
To see the AppData folder you'll need to enable View Hidden Items in File Explorer.

Download the installer package for Windows: https://forumcontent.paradoxplaza.com/emailsignatures/2020.14-win-prod.zip
Unpack the file you just downloaded and place the three files in the Steam folder for the game you're having issues with. If asked if you want to replace already existing files click "yes" - that's a sign you are in the right place!

- run steam.exe as the Windows Admin user

- run the game from the PLAY button in Steam

IF that doesn't help, in this folder are some .log files:
C:/users//AppData/Local/Paradox Interactive/launcher-v2/
Please attach them here.  

Hmm, I'm not confident the newer 2020.14 installer files got used there - are you sure you extracted them and placed them as described?

And ran steam.exe as the Windows Admin user?

You might also try setting dowser.exe to run as Admin.  

Users with low post counts cannot include links in their posts, as an anti-spam measure. Anything else is okay.  

This?
https://support.microsoft.com/en-us/help/17588/windows-fix-problems-that-block-programs-being-installed-or-removed