Severe lag and black screen when Minecraft (fullscreen) loses or regains focus – game forces 60Hz instead of 165Hz

Hi,
I'm experiencing severe lag and a black screen for about 5–10 seconds whenever fullscreen Minecraft loses or regains focus.

This is not limited to Alt+Tab. The issue also occurs when I simply click away from Minecraft (e.g., to a browser or second monitor) or click back into it. Basically, any time the Minecraft window changes focus, the system starts behaving strangely.

When this happens:

• The entire system becomes sluggish

• My second monitor freezes visually (but audio continues - watching YouTube or Twitch is impossible)

• Minecraft itself seems to continue running normally (sound is uninterrupted), but the display interaction causes everything else to stutter or hang

After testing, I suspect the problem is caused by Minecraft forcing an incorrect refresh rate in exclusive fullscreen mode.
My monitors are set to 165Hz, but Minecraft appears to drop to 60Hz when in fullscreen, which seems to cause conflicts when the game gains or loses focus.

I have tried several workarounds:

• Forcing the correct refresh rate via NVIDIA Control Panel

• Updating graphics drivers

• Using different Minecraft versions (the issue started when I switched from a laptop to a desktop around version 1.13)

None of these helped. The problem disappears entirely when I run Minecraft in windowed mode, but that's not a proper solution — the taskbar and window borders are distracting, and I’d prefer to play in fullscreen or have easy access to an borderless windowed mode.

I’d really appreciate it if this could be investigated. Ideally, Minecraft should correctly detect and use the monitor’s refresh rate in fullscreen, and losing or regaining window focus should not cause system-wide lag, freezing, or display issues.