Remember that the config you apply is applied 'to the dashboard', which then pushes it down to the device, once the two have trusted comms. You will indeed need to make sure that whatever is upstream of the MX, by way of NAT (your 5G router) and firewall rules enables / allows those comms. Dashboard advises you what you need to permit, under Help > Firewall info. If you're uplink comes via a mobile network, beware of the use of carrier grade NAT, by your mobile network provider, if you need to get VPN working to your MX.
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