About 10-11yrs ago, I bought a Wileyfox phone that was built on the Cyanagen fork of android. Far more privacy and security than any android based phone
Sadly, not enough people bought them and a few yrs later, they went out of business.
The OS still exists though, it forked into lineage OS.
But until manufacturers are forced to unlock devices to allow another OS to be installed, these are niche markets that require devices to be jail broken.
Once a device is no longer supported with OS and security updates, the law should dictate that they be unlocked and if a company goes out of business and stops support for devices, they must be made open source so that others can modify them to still be usable.... most devices have a use life long past their 'planned obsolescence'