FreeBSD is closer to Unix than Linux is

Question is how “real” that support is - firmware updates matter and depend mostly on the chip manufacturer’s support.

By 8 years old even the newest devices will be out of software support and using EOL phones is not a particularly great idea for security. GOS’s security focus goes out the window if you use an old version with known vulnerabilities.

You can probably expect GOS support as long as Google supports the device, that is the main limitation. For the newer Pixels that is promised to be 7 years after release.

Going by this table, Pixel 6 is currently the oldest to get full GOS updates

That matches Google’s software support

Don’t buy ASUS, they have a terrible security record. At this point I would trust only MikroTik and Ubiquiti.

All the kernel Rust code is GPL, so you can leave that slippery slope alone. MIT licenced core utils just leave the door open to eventually using them in the BSDs as well.