Hello Kathirvel,
Thank you for posting question on Microsoft Windows Forum!
Based on your query of being not able to uninstall “ Windows” mobile app in iOS.
Since the standard way is failing, the suggestion here is to bypass the home screen by using the Settings menu. Open the Settings app on your iPhone. Tap on General. Tap on iPhone Storage. (Wait a few seconds for the list of apps to load). Scroll down until you find the Windows app and tap on it. Tap Delete App at the bottom of the screen. Confirm the deletion when the pop-up appears.
If the iPhone still restarts or freezes. Try to force restart. This will clear the temporary cache and stops any background processes that might be clinging to the Windows app. Quickly press and release Volume Up. Quickly press and release Volume Down. Press and hold the Side Button until the Apple logo appears. Once it reboots, try the Settings method again. Also, In that same iPhone Storage menu mentioned above, try tapping Offload App first. This removes the app's "brain" but keeps its "memory" (data). Once offloaded, try tapping Delete App.
Hope the above information is helpful! If it helps you getting more insight into the issue, It is appreciated to consider clicking "Accept Answer". Should you have more questions, feel free to leave a message.