Okay... I got the root cause.
I updated my nvidia drivers. In the settings is the possibility to check 'optimal energy settings'. This setting limits the gpu dramatically. Mupen64, desmume, pcsx2, cemu, citra and even dolphin were affected. After changing the setting to max perfomance, the issues were gone. Vsync is working, performance is great, no glitches and freezes. Etc.
Unfortunately the default setting is optimal energy setting. So I can only recommend that everyone should check this setting.
I updated my nvidia drivers. In the settings is the possibility to check 'optimal energy settings'. This setting limits the gpu dramatically. Mupen64, desmume, pcsx2, cemu, citra and even dolphin were affected. After changing the setting to max perfomance, the issues were gone. Vsync is working, performance is great, no glitches and freezes. Etc.
Unfortunately the default setting is optimal energy setting. So I can only recommend that everyone should check this setting.