The effect of scrolling the mouse wheel is not immediate when hovering over the preview area, and mouse wheel is enabled by clicking rather than by hovering.
Hopefully, these new observations, using the paint tool, will help in tackling the issue.
Observations :
Initially, the mouse wheel is not associated with the radius slider. If the pointer is moved over the image preview area, the mouse wheel is ineffective in changing the brush radius.
Clicking inside the dialog box has no effect on the mouse wheel.
Clicking anywhere outside of the dialog box enables the mouse wheel to control the radius slider.
The mouse wheel stays enabled to control the radius slider even when the mouse crosshair or pointer hovers outside of the image preview area, for example over the dialog box.
Clicking the mouse over the main menu enables the mouse wheel to change the tool radius.
Clicking while the pointer is inside the tool dialog box disables the mouse wheel for radius control.
The smudge and clone tools have the same behavior.
Here is what I expected :
Immediately upon hovering over the image preview area, the mouse wheel should be enabled for controlling the brush radius.
When the mouse pointer is not hovering over the image preview panel, the mouse wheel should not control the radius.
I found the Windows 11 setting to fix it.
Under mouse settings, I had to enable "Mouse hover select" to remove the required first click. It now works as expected.