Are you sure your 4G network may block P2P? Usually they do not block P2P traffic. The problem might still be on the host router/firewall side.
Can you check what firewall you are using and check if Remotly.exe is not blocked for inbound/outbound P2P traffic? The best solution is to select some random port in Remotly server for inbound connections and make sure it is allowed by the firewall (add a rule for Remotly.exe for the selected port in Remotly Settings).
First of all, please check if there are any rules for Remotly.exe or RemotlyClient.bin in your firewall settings.