You can use this to find which devices can wake your PC:
for device in /sys/bus/usb/devices/*/power/wakeup; do
echo "$device - $(cat $device)"
done
And then for each of those run echo "disabled" | sudo tee /sys/bus/usb/devices/1-6/power/wakeup (where 1-6 is the device id).
You can add a service file like this at /etc/systemd/system/disable-usb-wake.service:
GNU nano 8.1 /etc/systemd/system/disable-usb-wake.service
[Unit]
Description=Disable USB Wake
After=suspend.target
[Service]
Type=oneshot
ExecStart=/bin/bash -c 'echo "disabled" | sudo tee /sys/bus/usb/devices/1-6/power/wakeup'
[Install]
WantedBy=suspend.target
then run sudo systemctl daemon-reload and sudo systemctl enable --now disable-usb-wake. Worked for me, hope it will work for you as well!