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 Router 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 Bridge 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 dnsmasq
• 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 WiFi is wlan0 while that for A8000 is wlan1
• 192.168.193.0 / 255.255.255.192 is allocated as the new 6GHz network with 192.168.193.62 as the access point
• 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 dnsmasq

Install the package by sudo apt-get install dnsmasq and add the following to /etc/dnsmasq.conf.

interface=wlan1
dhcp-range=192.168.193.1,192.168.193.61,12h

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/

Change the dhcpcd configuration in /etc/dhcpcd.conf such that wlan1 uses a static IP address instead of DHCP.

interface wlan1
static ip_address=192.168.193.62/26
nohook wpa_supplicant

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
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

Enable IPv4 forwarding when appropriate by adding the following to /etc/sysctl.d/routed-ap.conf.

net.ipv4.ip_forward=1

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