The simple way is to install the package
nm-tray and add it to the startup list of programs.
sudo apt install nm-tray
After a while the available wifi networks may become hidden with only the "active" and the "known" being displayed.
You can display them all again
by clicking on your network listed under "Wi-Fi connection(s)" or under "Known connection(s)" thus resetting the connection (disconnecting & re-connecting to the same network) and displaying the list.
by clicking on your network listed under "Active connection(s)" thus going offline and displaying the list
Another solution is
wicd. It is very reliable but a bit different from the normal panel tools. It takes some time to list the available networks as it scans for them, also it takes some time to connect after suspend. Another problem is that is seems to inhibit
networkmanager from running: logging out of Lxqt into Plasma while Wicd is not yet started there, you will have no network connection until Wicd is started.
After using Wicd for a while now I prefer nm-tray.