So the issue with this setup is that Synology (after DSM 7) locked down security on all the apps that run on it. In doing so they locked down the ability for these apps to be able to create routes. Long story short, you can access the NAS using TwinGate, but the NAS cannot access anything on TwinGate.
The one that you can use is TailScale. I wrote up a how to to make it easier to update!