Other than updating the screenshots so a new user isn't confused with trying to translate UI changes I don't see an issue.
Usually I manually create a bridge for my guest wifi if I'm not also doing the single bridge multiple vlans method? At least I've run into troubles if I don't create the bridge manually first?
Maybe there needs to be some changes on how the netmask is discussed when creating an interface.
Anyway. It should be relatively straightforward to fix. I might just copy the screenshots/additional instructions from how I said to make a separate SSID on separate bridge. Only addition is to make sure forwarding works as that didn't matter in the below example.