Can I limit / choose the channels my Wifi uses to connect in my WLAN under Linux?

Answer

Yes, that is done inside of the supplicant.conf configuration file.

This example shows how to only set to 2.4GHz channels for ETSI domain.

 ctrl_interface=/var/run/wpa_supplicant update_config=1 freq_list=2412 2417 2422 2427 2432 2437 2442 2447 2452 2457 2462 2467 2472   network={         ssid="test"         psk=0123456789         proto=RSN         key_mgmt=WPA-PSK         auth_alg=OPEN }

Of course if the radio also supports the 5Ghz band, 5GHz frequencies (5180, 5200, ...) can also be chosen here.

Note: if this is being done on a 5GHz radio and only 2.4GHz channels are selceted it is not a warranty that the radio will never transmit at 5GHz. Hence, above cannot be used as a method to disable 5GHz on a given radio.