HJ

I would like to add to my comment that the cursor also moves to the taskbar when the application is maximised but not in full screen or when the application window is made slightly smaller.

Experiencing a similar issue too.
As of the recent update to v1.21.121, the application will not entirely lock the cursor whilst playing, so when turning your camera far enough in a certain direction, this causes it to move just slightly out of the application window although in full screen. Therefore, when attempting to interact with the game through left or right clicking, it will cause the game to pause as somewhere outside of Minecraft has been interacted with.

This seems to only occur to me when I turn my camera (in-game) to the left, far enough to cause the issue to arise. This may be because of my second monitor on my left which I can see the mouse move just slightly to.

Here’s what I can see on my second monitor:

The issue didn’t seem to arise when I manually made the window smaller or maximised so it wasn’t full screen.

However, I tested Juliee’s issue of the game crashing on full screen toggle but this issue doesn’t occur for me.

OS: Windows 11
2 Monitors
Minecraft v1.21.121
Issue occurs when in: Full Screen
Written 8/11/2025 - (DMY)

Same issue here, having ‘Improved Input Response’ enabled causes the amount of memory Minecraft.Windows uses after just joining a world / realm to increase rapidly - to around 26 GB on my 32 GB memory.
I found your solution of disabling ‘Improved Input Response’ and restarting the application to have solved the issue resulting at a stable use memory of around 2.4 GB. I did not change my memory tier and it seemed to fix the issue.
This situation first occurred to me after the update to v1.21.120.
(Done on Windows 11)

Same issue, slowly increases but significantly increases when I join a world / realm, frames decrease too.

Windows 11, Minecraft Version 1.21.120