My apologies for not being clear as I was on my phone, and not easy for me to type a lot...I forget to mention that also ,but on 2.4GHz OFDMA/MU-MIMO is disabled by defaults
The way I see it there are two possibilities, 2.4 is no longer broadcasting, or the devices can not see the broadcast. Since you mention specifically Sonos I suspect that it is still broadcasting.
IF it is off, please try turning it on.