My pet peeve about all these small single board computers is that none of them have multiple ethernet ports, which severely limits their usefulness as networking hardware. They'd otherwise be very well suited to being various kinds of packet routing appliances.
You can sometimes hang a usb ethernet dongle off them but performance on those tend to be somewhat limited.
Check out solidrun, they have a variety of boards with multiple Ethernet ports.
I used to wonder why embedded boards didn’t have multiple Ethernet boards and why it’s not common to use ethernet to connect to peripherals instead of “old interfaces”. Until I tried it for a project. It turns out Ethernet uses roughly 0.5 to 2W per port depending on speed (that’s 1-4W per connection).
Perhaps what you want is a range of boards with many combinations of features. Some with 4xethernet, some with 2xethernet, some with PCIE and 1xethernet, some with M.2 and PCIE, some with M.2 and 2xethernet, etc. to fill out that big matrix of combinations. But is the market big enough for such a huge range to be economical?
Some of them have PCIE which you could connect a network card to. That seems like a more practical way to allow flexibility than having a lot of special purpose boards.
You can sometimes hang a usb ethernet dongle off them but performance on those tend to be somewhat limited.