BepInEx is coded in mono and C#, Unity Explorer is a GUI made for exploring the live code while the game is running.
Absolutely nothing to do with Visual Studio,
although you most definitely need vcredist on your PC to run most games.
The default key to open the explorer should be F7, but it should also pop up on it's own during boot up.
The instructions are clear as day, open the explorer, click on "demo", and click the big red destroy button to remove the pop-up message. Unfortunately this is hard coded per day after day 8, so you will have to destroy it over and over again.
Also, this should be the demosaic for the build on OP, (link may expire)
You must be registered to see the links
I think some of the texturing is still filtered, so I will look into the textures at some point if I get bored enough.