Setup:

1) Connect ethernet cable.

2) Install Proxmox 8-x.x.

3) After the install completes and the system has rebooted, install wpasupplicant (and install vim while you're at it):

Code:
apt update && apt install wpasupplicant vim
systemctl disable wpa_supplicant

4) Configure wpasupplicant:

Code:
wpa_passphrase SSIDNAME PASSWORD >> /etc/wpa_supplicant/wpa_supplicant.conf

5) Determine wireless adapter device name:

Code:
root@px1:~# dmesg | grep wlp OR grep wlo
[    4.374531] iwlwifi 0000:04:00.0 wlp4s0: renamed from wlan0

6) Create /etc/systemd/system/wpa_supplicant.service and add configuration (specify YOUR wireless interface on the ExecStart line):

touch /etc/systemd/system/wpa_supplicant.service

Code:
[Unit]
Description=WPA supplicant
Before=network.target
After=dbus.service
Wants=network.target
IgnoreOnIsolate=true
 
[Service]
Type=dbus
BusName=fi.w1.wpa_supplicant1
ExecStart=/sbin/wpa_supplicant -u -s -c /etc/wpa_supplicant/wpa_supplicant.conf -i wlp4s0
Restart=always
 
[Install]
WantedBy=multi-user.target
Alias=dbus-fi.w1.wpa_supplicant1.service

7) Enable wpasupplicant service:

systemctl enable wpa_supplicant

8) Configure /etc/network/interfaces:

Code:
auto lo
iface lo inet loopback

iface enp1s0 inet manual

auto wlp4s0
iface wlp4s0 inet manual
    address 192.168.1.100/24
    gateway 192.168.1.1

auto vmbr0
iface vmbr0 inet static
    address 192.168.2.1/24
    bridge-ports none
    bridge-stp off
    bridge-fd 0

source /etc/network/interfaces.d/*

9) Restart wpa_supplicant and networking services to connect wireless adapter to wifi network:

systemctl restart wpa_supplicant && systemctl restart networking