If you don’t want to tinker with a Raspberry Pi, a simpler alternative would be AdGuard DNS

https://adguard-dns.io/en/public-dns.html
(Configure manually -> Routers)

OpenRCT2

An open source re-implementation of RollerCoaster Tycoon 2

Link to the repo:
https://github.com/polymorphicshade/Tubular

It looks like it’s not open source.

You might want to post this in a Linux community then instead of the open source community

Had to look it up too, looks like a way to choose your own push service:

https://unifiedpush.org/

And if you start eating a properly wrapped one, it turns into a quiche 🤔