How to check P2P connection between two devices?

Hi, my master model includes 2 devices A and B.
+, At device A I use 1 lte 4g wifi dongle. I don’t see “Client Isolation” and “UPnP” settings.
+, At device B I use a wifi router. I have checked the configuration of this router with the following parameters:
., Firewall network: enable port 9993 - UDP, TCP - ZeroTier
., Advanced wireless network : disable “Activate customer isolation”
., Forwarding router: UPnP enable for Zerotier
Two devices A and B can still communicate with each other, but the link quality is low. Is there any way to fix this problem? Thank you.
The link I referenced earlier: High ping to any peer