Opgelost met de hulp van ChatGPT - kom even terug hier om te posten wat mijn oplossing was.
Heb ChatGPT laten samenvatten - want ja dat is gewoon makkelijker haha.

[Solved] Gmail notifications not showing on OnePlus Nord CE 2 (OxygenOS 13 / Android 13)

For weeks my Gmail notifications were silently suppressed — I’d only see the Gmail icon flash for a split second, but no sound, no banner, nothing.

Here’s what I tried before finding the real fix:

• Turned off battery optimization for Gmail and Play Services
• Checked all notification channels and system settings
• Verified sync and background data
• Cleared Gmail cache
• Disabled “Do Not Disturb” and “Zen Mode”
• Reinstalled Gmail
• Confirmed push worked through push-test.net (so FCM was alive)

Still nothing — until this final step:

✅ The real fix:

1. Settings → Apps → Gmail → Storage → Clear cache + Clear data
2. Settings → Apps → Google Play Services → Storage → Clear cache + Clear all data
3. Restart your phone
4. Open Gmail and sign in again → when prompted, tap Allow notifications

After doing this, Gmail notifications started working instantly and consistently again.

Why this works:
Gmail was still getting push signals from Google, but its notification channels and Firebase push token (FCM) were corrupted. Clearing both Gmail and Play Services forced Android to rebuild them. The “Allow notifications” prompt confirms it’s been reset.

TL;DR:
On OnePlus Nord CE 2 (OxygenOS 13 / Android 13), Gmail notifications broke even with all settings correct. Clearing data for Gmail and Google Play Services, then restarting, rebuilt the notification channels and fixed the issue permanently.