Some months ago, I used Tailscale to remotely connect to a PC with B4A installed (my PC was at home) using my phone. Both my home PC and my phone were on the same Tailscale network.
It worked perfectly. Tips:
The phone must be connected to Wi-Fi
Tailscale must be active
B4ABridge on your phone will show the IP address from the Wi-Fi network, not the Tailscale IP assigned to your phone, but it will work anyway
The Connect menu in B4A will NOT show the Tailscale IP assigned to your phone; you will have to manually type the IP address assigned by Tailscale to your phone using the 'New IP' menu item
I have successfully connected B4ABridge with my home computer when I was using TailScale in the past. B4ABridge reports that it is not connected but it is and it works. Either way B4ABridge is a port listening and it does not matter at all how you will get there. What it matters is to connect to this port.