Nice way to capture the CO2 and we could generate the electricity by burning cows.

This is what Layer 3 is for. You need to open the relevant port between vlans (e.g. TCP 443 for https) on the firewall. I think its UDP 1900 but may vary by appliance.

I’d also allow multicast, ICMP (ping) and DNS between your vlans as a minimum depending on what they’re used for.

I used to use all the Simple tools, even paid for them, unfortunately the dev changed monetization to a shitty model and I got locked out.

Since then I moved to QKSMS. Its on F-Droid and despite some initial quirks I’m very happy with it.