How to Start Desktop Game in Fullscreen?

Hi all, this is a question for anyone who makes desktop games for Steam, itch.io etc. I would say it is normally an expectation of players that a desktop game starts in fullscreen (or at least has the option to).

I have always used a function to request fullscreen when the game starts, this has worked in C2 and C3 for approximately 6 years without a single issue, however for whatever reason it no longer works since I updated to r210.

So I wondered how other people achieve this?

As I said on the linked thread, thanks so much for the advice!