The managed switch is for situations where you need wired clients to be members of a VLAN and your AiMesh nodes don't support wired VLAN tagging. I don't remember off the top of my head your specific setup as it's been awhile since I've been in this thread, but an AiMesh node can't magically make an unmanaged switch start VLAN tagging traffic so the switch isn't playing a part at all in your VLAN setup.
I was under the impression that "Guest Network = VLAN", regardless of Ethernet vs. WiFi, because when a guest network is created, so is the VLAN. Even Asus Support stated that a managed switch is REQUIRED for Guest Network/VLAN support (but I do take what they say with a grain of salt).RT-AX57 Go runs 3006 firmware with Guest Network Pro support.