Windows: Strange Alt-Tab behavior

[Dpunkt]

Game running in fullscreen in Windows.

Wth WinAPI as graphics driver: Game "refuses" to go to background, but after some tries can be left. When going back to the game it starts to flicker between black and the actual game view. When this happend to me during a game, pausing the game seemd to help to fix it.

With SDL: Alt-Tab is very slow, but works on first try. going back to the game leads to the "game view" (very brief), then black (1s?) and than back to the actual game.

Behavior is the same in the menu screen, it is not required to run a game.

[Flamefire]

Game "refuses" to go to background, but after some tries can be left

I had trouble understanding what you meant by that. What I see: Atl-tab shows the new window in front of RTTR, so with smaller windows you can fully see and interact with RTTR.
Is that what you meant?
What do you mean by "can be left"?

I could not reproduce the "blackness" though. But I've seen erroneous behavior with ALT-TAB and fullscreen in other games.
The next build will include a border-less fullscreen mode option which works much better with that.

[Dpunkt]

I tried alt-tab and windows-m, but the game stayed in foreground.

[Dpunkt]

I did some tests:

The issue only occured on my notebook with Intel I5.10210U CPUs Intel UHD Graphics. I did not see any issues on my PC with Nvidia GPU.

Borderless window with SDL only uses the Screen above the taskbar, with WinAPI the full screen is used, like in fullscreen (on both GPUs).

On the Intel GPU with WinAPI selected, the issue stays the same with borderless window (compared to fullscreen) : Flickering when going back to the game. It seems to randomly show black, old and the current frame. I tried to record this with obs, but it just showed solid black instead of the flicker.

With SDL "borderless window" solved the issue (no delay when entering and leaving the game), but the taskbar ruins the game experience.

With SDL Fullscreen, the notebook seems to switch resolutions when entering and leaving the game. I can see the screen switching of completely for a brief moment, in total this took 1-2 seconds when leaving or entering the game. The resolution is configured correctly. On older games I would have guessed color depth.