Guest Network with no Internet access on DSA 21.02

Installing and Using OpenWrt Network and Wireless Configuration
5

There's your problem.
Create bridge device & assign your Fire interface to it. Without that OpenWrt:

  1. has no L2 interface to assign 192.168.73.1 to
  2. has no L2 bridge to attach wlan0-1 to

You can easily create bridge device in LuCI. It should give you something like

config device
        option name 'guest'
        option type 'bridge'

then you need option device guest in your Fire interface.