I have tried this suggestion by writing this into /etc/config/wireless:
option channel 'auto'
option channels '124, 36'
Couple of questions:
I only ever got a radar warning once and before this test the router was happily using channel 124, whereas now it went straight to 36: is this normal?
I can't seem to find a corresponding GUI field in Luci, this isn't supported yet, right? (19.07.3)
Well, that was more than a year ago, when I was probably running 19.07.3.
With 21.02.1, the auto keyword behaves as expected, in conjunction with a channel list.