@DoubleteeApt
Well that's a loaded question.
Let's start with what kinds of connections you have, cellular, cable, fibre, dsl because each has unique properties and options...and almost all of them NAT by default (you'll know this when you check your WAN port Details and you get a private address instead of a public address). This for instance is a public IP on my WAN:
You'll know you're NAT'd if it starts with 10. or 192.168 (which are private IP ranges that are not routable on the internet). Private IPs make setting up an inbound VPN connection impossible (well, very non-trivial).
If the connection is NAT'd there are often options to bridge the router to the public IP (cable modems and dsl router often have a bridge mode which disables the internal router function and passes the public IP straight through to the first device that makes a DHCP request). LTE cellular modems do something similar, often called 'passthrough mode' instead of 'bridge mode'. Others, like GPON/FTTH allow PPPOE connections that can request their own public IPs even if the FTTH modem is NAT'ing. Like I said, loaded!
Next up is how you are treating those 3 connections, are they loadbalanced or failover.
Also of concern is if you are running a VPN server on each WAN port, or just one.
Lastly you should verify that whatever IP is assigned to the WAN port (temp disconnect the other 2 WANs) matches what you get when you browse to formyip,com or similar sites, then you know your ports will work properly.