I knew I will find this thread.
I can confirm I am facing the same issue on P7 Pro with the latest update.
Molly (using its own notification method), Simple Calendar Pro (afaik it uses its own method too), Whatsapp, Messenger Lite - either no notifications at all or VERY delayed and only when I open these apps manually. When I reboot the device, it shows all the missed notifications and then doesn't display new ones or displays with huge delays.
Battery is Unrestricted on all these apps/Google services.
This is certainly an update / Android 14 issue as all this was working perfectly fine prior to Android 14 update.