Installed Rogue Mage through GOG on PC and missed a couple parts of the tutorial. Is there a way to create a second game save or restart a game save, as there was in Thronebreaker?

This! I didn't even miss anything, it literally just skipped half the game for me with everything unlocked for some reason. As far as I can tell there's no way to delete progress within the game itself.

Hello, I know this post is old but it can help other people, to start a new game you need to delete the save
https://www.youtube.com/watch?v=I0qnS3GOCM0 this video shows how to do it

Posting a video seems extreme for something so simple.

Just post the save/profile folder & be done with it: %APPDATA%\..\LocalLow\CDProjektRED\RogueMage

The video is only 1 min long and it's more precise, but your way is good too yes