I’d like to create an isolated guest network on my 2927 router.
The DrayTek knowledge base describes 2 methods:

• Set the ‘Isolate LAN’ option for the Guest SSID
• Create a separate VLAN for the Guest network

Which method would you prefer?

Unless I miss my guess there is no "Isolate LAN" option in the router wifi setup - that only appears in the Access Points menu. So unless you are not setting this up on the router, as you say you are, your only choice is the separate subnet/VLAN. Best anyway imo.

My bad, the router has indeed no “Isolate LAN” option, only “Isolate Member”. I will isolate the member and then follow the step to setup a VLAN.