There aren’t, really. There are a few antiques and half baked things.
A big problem is that these days, unless you’re the size of Apple or Samsung, it’s impossible to get a reasonable hardware soc and modem other than one which only runs a soon obsolete blob laden android which is going to be EOL before you’ve even finished your design.
The hardware is not there. The firmware/hw data/platform isn’t there even to begin OS work with. And there’s a global shipping, regulation and mobile operator hell waiting on the other side. And a product lifecycle that’s only a few years long.