install packages:

apt install --no-install-recommends tigervnc-standalone-server tigervnc-tools supervisor xfce4 xfce4-terminal xterm dbus-x11 libdbus-glib-1-2
apt purge pm-utils *screensaver*

create systemd service:

cat > /etc/systemd/system/[email protected] << EOF
[Unit]
Description=Start TigerVNC server at startup
After=syslog.target network.target

[Service]
Type=simple
User=user
Group=user
WorkingDirectory=/home/user

PIDFile=/home/user/.vnc/%H:590%i.pid
ExecStartPre=-/bin/sh -c "/usr/bin/vncserver -kill :%i > /dev/null 2>&1"
ExecStart=/usr/bin/vncserver -fg -depth 24 -geometry 1920x1080 :%i
ExecStop=/usr/bin/vncserver -kill :%i

[Install]
WantedBy=multi-user.target
EOF

setup xstartup per user:

mkdir -p ~/.vnc
cat > ~/.vnc/xstartup << EOF
#!/bin/sh
unset SESSION_MANAGER
unset DBUS_SESSION_BUS_ADDRESS
startxfce4
EOF
chmod +x ~/.vnc/xstartup

setup tigervnc per user:

mkdir -p ~/.config/tigervnc
vncserver