The use of 6GHz WiFi band has been approved in Japan since September 2022.
This article (Japanese) provides detailed instructions to build a 6GHz WiFi Bridge Mode AP there, using a Raspberry Pi and a Netgear A8000.
It is most likely that these instructions are applicable in any country where the use of 6GHz is allowed. However, it is not tested outside of Japan.
Instructions to build a 6GHz client is covered by a separate article How to build a 6GHz WiFi client with a Raspberry Pi and Netgear A8000.

Also, it might be useful to take a look at another AP article, How to build a 6GHz WiFi Router Mode AP with a Raspberry Pi and Netgear A8000.

Task Summary

• Force the standard mt7921u driver to recognize A8000
• Refresh Linux Wireless Regulatory Database to reflect the addition of 6GHz band WiFi
• Renew MediaTek WiFi firmware
• Install bridge-utils
• Install hostapd and upgrade it to v2.10

Prerequisites and Assumptions

• Raspberry Pi OS version is Bullseye, i.e., kernel 6.1
• Interface name for the onboard wired LAN is eth0, that for the onboard WiFi is wlan0, and that for A8000 is wlan1
• Raspberry Pi is wired to an upstream router, e.g. ONU, where DHCP service is available
• Instructions described in this article are for Japan

Force the standard mt7921u driver to recognize A8000

Refer to How to build a 6GHz WiFi clinet with a Raspberry Pi and Netgear A8000

Refresh Linux Wireless Regulatory Database to reflect the addition of 6GHz band WiFi

Refer to How to build a 6GHz WiFi clinet with a Raspberry Pi and Netgear A8000

Renew MediaTek WiFi firmware

Refer to How to build a 6GHz WiFi clinet with a Raspberry Pi and Netgear A8000

Install bridge-utils

Install the package by sudo apt-get install bridge-utils and areate a new file /etc/network/interfaces.d/bridge.conf as follows.

auto br0 iface br0 inet dhcp bridge_ports eth0 wlan1 

Install hostapd and upgrade it to v2.10

Install the package by sudo apt-get install hostapd.
Then upgrade it to v2.10 as 802.11ax support was only added in v2.10. Since WPA Applicant is also have to be upgraded to v2.10 for client, let's download hostap_2_10.tar.gz package that incorporate both WPA Supplicant and hostapd from its distribution site.

tar -xzvf hostap_2_10.tar.gz cd hostap_2_10/hostapd cp defconfig .config echo CONFIG_IEEE80211AX=y >> .config echo CONFIG_IEEE80211AC=y >> .config echo CONFIG_SAE=y >> .config echo CONFIG_ACS=y >> .config make sudo mv /usr/sbin/hostapd /usr/sbin/hostapd_2_9 sudo cp hostapd /usr/sbin/ sudo mv /usr/sbin/hostapd_cli /usr/sbin/hostapd_cli_2_9 sudo cp hostapd_cli /usr/sbin/ 

Create a new file /etc/hostapd/hostapd.conf. Do not forget to change ssid=, sae_password=, and channel= appropriately.

ctrl_interface=/var/run/hostapd ctrl_interface_group=0 country_code=JP interface=wlan1 bridge=br0 driver=nl80211 ssid=foo-ax sae_password=foobar hw_mode=a channel=57 ieee80211ax=1 wmm_enabled=1 op_class=131 ieee80211w=2 auth_algs=3 wpa=2 wpa_key_mgmt=SAE rsn_pairwise=CCMP rsn_preauth=1 sae_require_mfp=1 sae_pwe=1 wpa_group_rekey=1800 group_cipher=CCMP wpa_psk_radius=0 

Register hostapd as a service that automatically starts at boot.

sudo systemctl unmask hostapd.service sudo systemctl enable hostapd.service 

You can optionally disable the use of wlan0/onboard WiFi by sudo iwconfig wlan0 txpower off.

Done

See if you are on 6GHz by sudo hostapd_cli status.

$ sudo hostapd_cli status Selected interface 'wlan1' state=ENABLED phy=phy1 freq=6235 num_sta_non_erp=0 num_sta_no_short_slot_time=1 num_sta_no_short_preamble=1 olbc=0 num_sta_ht_no_gf=0 num_sta_no_ht=1 num_sta_ht_20_mhz=0 num_sta_ht40_intolerant=0 olbc_ht=0 ht_op_mode=0x0 cac_time_seconds=0 cac_time_left_seconds=N/A channel=57 edmg_enable=0 edmg_channel=0 secondary_channel=0 ieee80211n=0 ieee80211ac=0 ieee80211ax=1 beacon_int=100 dtim_period=2 he_oper_chwidth=0 he_oper_centr_freq_seg0_idx=0 he_oper_centr_freq_seg1_idx=0 supported_rates=0c 12 18 24 30 48 60 6c max_txpower=23 bss[0]=wlan1 bssid[0]=94:18:65:xx:xx:xx ssid[0]=foo-ax num_sta[0]=1