I've given up on custom ROMs. There's always only an extremely limited set of devices that are supported, and those devices are EOL rather too quickly, forcing us to use custom builds from someone not directly affiliated with the project.

To be clear, not one of the Android devices I've purchased have ever had official support. I'm using a Samsung a8 at the moment.

I hope the custom rom community finds a better mechanism for providing better device coverage.

Are you aware of a current model phone that is officially supported by lineageos?

The "Linux" kernel even in something like LineageOS is heavily forked and in practically every case relies on userspace binary blobs for critically-important functionality. It's a far cry from what you can run on PC's, although postmarketOS is moving towards that goal. BTW it's not like Android itself is to blame for this, since other varieties of embedded Linux (by and large) are the same deal; the buck stops with SoC- and embedded-hardware manufacturers.

There is. You just don't want to spend the money or use the phones/tablets from said competitor.

postmarketos is beginning to support cellular capabilities. You may not have to wait a whole lot longer.