That's what I do. All my IOT stuff that I can't get wired or via Zigbee/Z-Wave goes on a separate VLAN along with my Home Assistant server. I have an mDNS repeater for ease of access to TV stuff via apps (might spin TVs off into its own VLAN, just haven't gotten around to it) but a 1-way firewall rule that only allows the main network to initiate connections. Certain devices which don't need internet at all get static IPs and completely firewalled.

Vlans are virtual lans. So no extra equipment, but your router (as minimum) must support them. If your AP also supports them, you send two vlan through one cable (trunking), and attach each vlan to its own SSID on the AP. There will be no connection between devices on SSID1/Vlan1 and devices on SSID2/vlan2. It’s like you have two cables. To make a connection between those devices you must tell your router to forward the packets between the virtual lans.

That’s the whole trick - you see one cable, but inside it’s like 4000 cables. It’s the same inside your switch/router with vlan support - you see one physical port, but it’s 4000 inside - one for each of the 4000 cables. Each one works and behaves like a physical one. You get data in from one, and can forward it upstream to internet or into one of the other nic’s/cables as that’s what a router does