Hello again Bruce,
As I said in my earlier post about bricking my Beryl-AX with an OpenWrt firmware upgrade, what I was actually wanting to do was exactly this ^. Get all LAN traffic to go through Tailscale and thence to remote exit node. As with Aleksandr here, my Tailscale network is fine. But choosing a "custom exit node" in the tailscale instance on the Beryl causes loss of internet access from the Beryl. I have tried pretty much all of what has been suggested here without success.