Microsoft’s Wolverine for the TCP stack was not available until Windows 3.11. An argument could be made that these systems are defacto air-gapped as they cannot communicate with modern networking.

Not 6E but the GLINet Flint 2 runs a flavour of OpenWrt 23.05.

I own the original Flint and I have been really happy with it. It’s has a “fisher price” mode for most people; but then you can also log into Luci and really tinker under the hood.