Hello and welcome to the community. 
Seeing as it is a new PC, it’s probably missing .NET Framework. Since at least Windows 8 onwards, Windows Update is well-known to forget to install or update .NET Framework. Especially on newer PCs and first-time installations on machines. Microsoft never bothered fixing it, and since we’ve been waiting 11 years for them to fix it now - don’t hold your breath.
You need a minimum of version 4.7.2, but the latest version (4.8.1) is recommended.
You can manually download and install it from the official Microsoft .NET website here: Download .NET Framework | Free official downloads.
If you get told you already have .NET framework, choose the repair option in the installer to fix whatever parts of it Windows Update potentially messed up.
Still an issue after that?
- What games are having the issue?
- Are they all bought from Steam? Or are some cracked/pirated Steam versions?
- Are the games installed anywhere else other than the default C:, is it internal or external?