When you have MikroTik accesspoints or other types that can be configured with different SSID going to different VLAN, you could still consider using VLANs.
Remember, when you have totally dumb switches they can often transport VLAN without issue. Only test if they allow 1504 byte MTU (extra 4 bytes for the VLAN tag).
Then you can put your WiFi guests on a tagged VLAN and put a VLAN subinterface in the router to handle that traffic, and it will still be isolated from the LAN because the guests are unable to send untagged traffic.
However, beware that Windows device drivers are often buggy and they will untag and merge all traffic on receive.
So, do not put IPv6 on your guest VLAN or Windows will see the RA and assign itself an IPv6 address from the guest network.
For IPv4 with DHCP this isn't a problem because the DHCP address assignment is a request-response mechanism and systems on the LAN will be unable to make the request.
(unless of course someone adds a tagged VLAN interface on the machine)
VLAN capable managable switches make it all much more reliable because you can specify what traffic goes to what port(s) and if it is tagged or not.