Personally, I use https://unifiedpush.org/ via https://github.com/binwiederhier/ntfy app on my phone which lets you receive and distribute push notifications to any app that speaks unified push. Dev-friendly intro for Android here: https://unifiedpush.org/developers/android/.
I run my own self-hosted ntfy server, but people who don't want to do that but prefer to support a really nice OSS project than to bend over for Google can use ntfy pro for a small monthly fee: https://ntfy.sh/app