Sure, if I don't forget I will try more tests one of these days and report back.
I was playing around with 80 and 160 MHz on different channels and noticed something interesting.
When I select 160 MHz and set the channel to 149 or higher the wireless overview shows the corresponding frequency somewhere in the 6 GHz band (channel 165 as 6.775 GHz, suggesting WiFi 6E?!). My WiFi 5/6 devices can't see the network at all anymore, unfortunately I can't tell if it's actually transmitting at 6 GHz as I don't have any 6E devices yet.
So far I found one post mentioning this on a different MTK chipset, but it seems the other way round than what I see:
No problem for me though, I can set 160 MHz on channels 100 - 128 where it seems to work normally.