best bet is currently GrapheneOS and that is still Adroid and will likely have to fight an up-hill battle in coming years

there are some (decent & serious) Efforts to make Linux apps/UI tools phone format compatible

but for various reasons (mostly hardware) stuff like e.g. the Libre phone feel more like toys for enthusiast and very committed people then things a "average" person can just use.

The biggest problem in the future seems to be the regulatory capture/lobby induced "well meant but bad done" laws, wrt. to misguided device attestation laws which "happen" to in effect require you to have a Google Android or iPhone in practice even through that not actually being needed for the law to work.

Reach out to Fulu, this should be a project.

https://www.fulu.org/contact-us