2 correctly set monitors?

I have now got a 2nd screen for my PC. Now I have the following problem: I'm playing Minecraft Multiplayer on my main screen. But if I now press Eec and press Firefox with the mouse on my other screen, he taps minecraft and I have to press Minecraft again to return to the game. But not once but whenever I press something on my other screen, he taps it out. What do I have to do to stay in the game.

As far as I know, this is completely normal with Windows 10, and as far as I know it can't be changed. It also annoys me myself when I use OBS, for example.

You can try setting the window mode without a frame in the game. If that doesn't work either, Minecraft doesn't generally work because it varies from game to game.