hostapd

hostapd is a simple way to start a wireless access point, using any WiFi adapter. Install the Debian package;

sudo apt install hostapd

Enter the following into /etc/hostapd/hostapd.conf. The ‘bridge=’ line bridges the wireless interface to a bridge defined in the system’s netplan configuration;

interface=wlan0
ssid=YourChosenSSID
wpa_passphrase=YourChosenPassphrase
wpa=2
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
hw_mode=g
channel=11
wmm_enabled=0
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
rsn_pairwise=CCMP
bridge=br3

Start hostapd in the foreground;

/usr/sbin/hostapd -P /run/hostapd.pid /etc/hostapd/hostapd.conf

Alternatively, add the -B flag to start hostapd in the background;

/usr/sbin/hostapd -P /run/hostapd.pid /etc/hostapd/hostapd.conf -B

Hostapd can be started on system startup with a systemd unit, such as;

[Unit]
Description=hostapd

[Service]
ExecStart=hostapd -P /run/hostapd.pid /etc/hostapd/hostapd.conf
User=root
Group=root

[Install]
WantedBy=multi-user.target