OK. Looking further at what you were seeing, the 100.124.x.x address is part of the Carrier Grade NAT address space. So while your WAN IP is 68.5.x.x, that IP is shared by others as well. Your connection has an additional NAT that translates to 100.124.x.x which is likely what you see on your router as the WAN address.
Unfortunately, I am unable to comment much further as I have not used TailScale and am ignorant of how it works. I believe it works by connecting you to home through an intermediate server since you don’t have a public IP address on your router. If I were to guess, it looks like you are connecting correctly as the 100.124.x.x address would not be reachable from outside your ISP’s network. I should have looked up that address space previously.
Perhaps someone else here who knows more about Tailscale can help you further. I’d be blowing smoke if I gave you any more advice. Sorry.. 