So I always here about on how Google Android and IOS those companies can see all your notifications. This is because to show a notification it calls an API.
Is there any technical reason that it has to send your notification data to Google and Apple or is it just to get more data on you?
Ntfy exists. I use it for 3-4 apps.
How do you get it to do discord and other random apps?
Can’t do it with random apps, but most FOSS apps, like Molly (fork of Signal), Element (matrix protocol), Tusky (for Mastodon), etc. use this.
I think using it for discord can be possible, but you would have to set up your own notification server. Like for Signal chats, there has to be another server between my notification server and Signal’s server (MollySocket), which listens to the notifications and sends it to my Ntfy. You will have to set something up that is always online waiting for new messages, and when new message arrives, it pings your Ntfy, and Ntfy pings your phone.