In fact using Roon remotely works quite well. I have succeeded to use it using the following configuration.
Roon server 1.6 on a Synology DS918 with 16TB HD + 1 TB SSD USB for the Roon database. I run a the Synology VPN server with L2TP/IPSec configuration with the standard configuration. It works also with OpenVPN (but you need additional software for connexion with the Mac or the iPhone).
My home is connected to internet with optical fibre 1GB(800MB/200MB). The synology is wired by Ethernet connexion directly to the Router (Icotera) provided by the FAI. My main system is a BlueSound Node 2i streamer connected by wire (RJ45 cat 5) to the home network. Node is also connected to a Heed Abacus DAC. From work I listen to roon from a Mac 10.14.5 using the standard Apple VPN connexion to my VPN. Roon has no difficulty recognising the home network and connecting to Roon server. I can listen to all my music and Qobuz without a glitch at any resolution.
With my iPhone 5S no problem either on a 4G network even travelling from home to work by car. But you need good network for that. I leave in a quite hilly area and sometimes it stops as there no or very small buffering in the Roon App. I must say the quality of the music is far ahead using Roon in my car. The phone connected to the car DAC with an Apple lightning cable.
At the beginning the phone had difficulties (Roon app) to recognise the Roon server. But since I specified the synology IP nb to the app (in the help section when not working), it is always recognised.
I can give more details if needed.