The second game which is invisible on launch, it's now asking me to allow it to make changes when I launch it but saying the publisher is unknown, and I tried to change it to window mode, it shows up as a small vertical line on the screen.
When running a steam game if prerequisites are needed it will ask if you want to make changes installing
things, directx ,dot net and may also change display settings and how the game can utilize the system.
Get used to it as your game library grows and this can happen every time that game starts up,
The game may have some settings you can set as a launch option from the game properties to
make it start thy way you want, google how to run game name in window mode.
Thee small line means it could be outbuting on another gpu, or is just minimized, try to click on
the line.