AFAIK Modern Android (>= 8.0) reserves the right to kill your app when running in the background unless there's a foreground toast bound (even then, can still be killed in low memory situations). How does this solution work around that? Is there a need to opt into the legacy "battery saver disabled" mode for the app which more closely mirrors <= 7.0 execution model?
Most distributors both show a foreground notification at all times and require exempting them from battery optimization. Because of its efficient design, something like ntfy only uses a few percent of battery per day [1].
System-level integration into Android ROMs would eliminate the need for those things.
I haven't seen any complaints, but folks who set this up are usually used to having persistent notifications (I currently have 6) without Google services.
At least I replaced the one from my Matrix client with the UnifiedPush-enabled ntfy. Hopefully it'll replace Signal too at some point. KDE Connect? Why not. K-9 mail? I hope, but that would require JMAP or IMAP adjustments.
One option would be to install the distributor as a system app.