GrapheneOS is currently the blessed child. Like CyanogenMod previously. They are "permitted" to access to Google Play Services because their work hardening Android currently benefits Google.
Once Google feels like there is sufficient stability and compatibility with hardened memory allocator and tagged memory (and when they can get Qualcomm to support it across their range), they will make harder, until impossible, for Graphene.
An old article [1] but:
> Google’s Android—and [Open Handset Alliance] members are contractually prohibited from building non-Google approved devices
So to compete you'd have to create a compatible Google Play Services as well as find a supporting manufacturer. Samsung managed their own competing apps and store [2] for a while along with Tizen, likely for leverage or theoretical pivot. But has since dropped that effort.
[1] https://arstechnica.com/gadgets/2018/07/googles-iron-grip-on...
[2] https://arstechnica.com/tech-policy/2021/07/google-bought-of...