I'm playing Pinball Fantasies on a new computer. The game is running on Linux (Mint 19.3). I'm experiencing a strange issue: when I push one of the controls, the game reacts correctly to it, but after about 2 seconds the flipper goes down, even though the key is still pushed. I never had that issue on the old computer (isntalled on both windows and linux systems). The issues only appears within the game, doesn't look like to be a problem with the OS keyboard settings.
Does anybody has an idea how to fix that?
Thank you :)

No, but I do have some suggestions. Check if you have sticky keys or some other sort of "assistive technology" enabled in your desktop environment. Turn it off if so; sometimes they use long modifier keypresses to mean "auto-enable", which in turn makes it start acting weird. Otherwise, it may be that you somehow got key repetition turned on for modifiers (I have no idea how that might happen). For that, try "xset -r" to turn off all autorepeat (and "xset r" to turn it on again, later). Unfortunately, desktop environments may override this, too, as they pretty much take over all settings whether you like it or not. I don't use a "modern desktop environment", so I can't really say any more. I doubt it's your dosbox configuration or base keyboard mapping.

Thank you for the input, unfortunatelly the ideas didn't help. But now I have some ideas where to look.
I'm using an Thinkpad, maybe the issue might be linked with the machine settings. I tried the game in a VM and there the issue was the same.