1. Will my app work fine in all devices though I didnt target API 35

No.
As in this article on Android Developers Blog, 16KB paged device won't be able to run your 4KB paged app.

2. Also, will google play accept to release an update of this app targeting API 34 after Nov 1st.

No.
From this Google Play guide document about target API level requirement,

New apps and app updates must target Android 15 (API level 35) or higher to be submitted to Google Play

3. Post this, How can I verify my app is compatible with 16kb memory page in Windows VS2022.

By using MAUI 9.
MAUI 8 is out of support, so if you want to just make it 16kb without migration, seems you're out of luck.
If your app also uses other native libraries, using APK analyzer on Android Studio would help updating your binaries.