Hello,
Apple doesn't provide any way to programmatically make a window gain focus or stay always in the forefront on the MAC catalyst platform.
For getting focus so that the window is at the top, this is explained How to activate a window in .net maui on Mac Catalyst.
First of all, I would like to inform you that the user has to touch the screen to active a session on iOS/MacCatalyst. Please watch the Apple's Window Management in Your Multitasking App video around 4:50. Therefore, you cannot bring an existing window to the foreground programmatically.
If you want the window to always be at the top, this FEATURE is also currently unavailable in MAC. You can keep an eye on this feature request in Add "Topmost" shell/app feature #8198.
Best Regards,
Alec Liu.
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