Hey All,
So I'm not sure this will work for everyone, but it did for me. My symptoms were very similar to OP. For context I have set up l2tp with IPSEC on my EdgerouterX. I could successfully connect with my iPad pro (from a remote cellular network) but could not with my macbook running Ventura. In MacOS I would try and initiate the VPN connection, it would try for a while and then eventually say it could not connect. On the edgerouterx side, the log entries get stuck on "***.***.***.*** is initiating a Main Mode IKE_SA".
I tried everything in the thread to no avail. In the EdgerouterX tutorial it says its optional to set MTU size. I looked up MTU size and decided on 1400. When I used the command "set l2tp remote-access mtu 1400" and then committed the changes, it suddenly started working.
Hopefully that'll help some folks.