Is there a solution for that? 

 https://unifiedpush.org  👀 

Maybe, you can probably release two versions of Damus Android in the future:
- Google Play version (using FCM)
- FOSS version (unifiedpush)

Amethyst have done that. 

 There's the ntfy app, but I didn't succeed to get it to work with amethyst yet.  

 Yes, it is known issue. I think Vitor and KotlinGeekDev has already aware of the issue and might prepare the bug fix later

https://github.com/vitorpamplona/amethyst/issues/688 

 On a not super related note (I’m assuming youre also using @GrapheneOS ): do you have recommendations for voip services that work well without google play services or do you prefer to just use your sim phone number for legacy calls/texts? 

 Signal, Simplex, jitsi all work great. 

 And if you want to shorten your SimpleX address you can do that at https://w3.do/ 

 My long SimpleX address turned into: https://w3.do/4fTrbJAI after I used https://w3.do to shorten it.  

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