This 2.4GHz during set-up is the same for most HomeKit devices AFAICT.
Here in the UK, my Meross smart plugs always need to use a 2.4GHz rather than 5Ghz just for their initial setup (after this initial setup, they work fine on a mixed 2.4+5 joint network).
My router is set as a joint 2.4+5Ghz network. So I just open my router’s settings interface in a browser, temporarily turn-off the 5Ghz connectivity setting, add the HomeKit devices, then turn the 5GHz setting back on. Done.
Yes, it’s a pain and Apple really should add a better thing for this, but at least it’s not too difficult to get done.