I have seen all over the internet that people (often) can't make notifications working.
So there's 3 steps that will make notifications work for sur !
Example for making WhatsApp notifications working
1. Security / Power / tap on Settings icon / and tap on "No linked launch when standby"
2. Security / Power / Standby Management : be sur WhatsApp is activate to be kept during standby (by default it is)
3. Security / Permissions / Auto-launched apps : be sur Whatsapp can auto launch (by default it can)
Nothing other is needed. All notifications now work.
Have a nice day.