This is mostly a duplicate of 802.11ax worse than 802.11ac with mt76 driver?
It is very interesting to see that you can reproduce this with intel ax200 as client, as most people with this problem had Apple devices.
The solutions that have been found to fix 802.11ax 80 MHz channel bandwidth so far are:
-
Remove
IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_160MHZ |in mt7915/init.c as does this pull-request to the mt76 wifi: mt76: mt7915: disable VHT CAP SUPP CHAN WIDTH 160Mhz for mt7915. This will remove 160 MHz VHT (802.11ac) bandwidth capabilities, which may be undesired.
There is also [MAC80211][mt76][remove mt7915 BW160 support] -
Some report switching to 160 MHz bandwidth solved their issue. To make this work, your client devices may have to support 160 MHz bandwidth. Not sure.
Maybe there are more solutions, which have not been published by Mediatek yet, but this is what is publicly known at the very moment about this problem.