First can you double check in Settings > Notifications > Advanced Settings > App Icon Badges >Toggle to On.
And tap On Notifications on App Icons.
If it's On try a soft reboot by turning the phone off and on.
Check within the app settings that Notifications are allowed.
If still no joy then as a troubleshooting step use Safe Mode.
> Safe Mode > https://www.samsung.com/uk/support/mobile-devices/how-to-start-my-galaxy-device-in-safe-mode/ turns off downloaded apps and themes etc which may highlight an app or theme that's causing conflict.
Another is > Clear Cache Files from the phone's System Partition Section > https://www.samsung.com/uk/support/mobile-devices/how-do-i-clear-the-cache-on-my-device/ You may need to insert your earphones or hook upto a powered On Laptop to access the Clear Partition Section. This may help with lag or stutters as this clears the phone of old/unused or broken cache files.There is also a Repair Apps option in the Menu System too.
Let us know how you get on please.
Daily Driver > Samsung Galaxy s²⁴ Ultra 512Gb ~ Titanium Black.The advice I offer is my own and does not represent Samsung’s position. I'm here to help. " This is the way. "