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’m still bitter about them removing the alarm function from the BBC radio sounds app

Late response but I got to the root of the issue. Lemmy (well, lemmy.world) wasn’t being cached by Quad9’s DNS servers.

I tested by using different DNS servers (OpenDNS) which worked fine, then permanently resolved it by installing unbound on my pihole and using that instead.

Tl;dr it was DNS

It’s always DNS

I already have them blocked