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.
Really enjoyed my experience with Tinykin. Very cute, very chill and easy enough to complete in a day or 100% over a weekend.
I keep dropping back into it so I’m sad to see it go.