For manga, I just use Suwayomi as a PWA, since I'm on iOS. Works really well for me. For books, I use openbooks, which automatically imports to calibre-web-automated, where I can then add the book to my Kobo shelf and have it sync to my Kobo. Also works really well for me.

That's really unfortunate to see. I was just getting around to setting up my alerts and thought ntfy looked great, since it supports instant notifications on iOS. I guess I'll leave it be until signal-cli-rest-api gets numberless support...