lubuntu extra apps website's methods not working!

The only apps in the PPA you mention are no longer relevant to anything Lubuntu supports.

The team that provides support are https://launchpad.net/~lubuntu-dev

Those apps were for very old releases of Lubuntu/LXDE which are no longer supported, as such the PPA was disabled and packages removed as they'll just create problems for Lubuntu users who will now be using the modern LXQt desktop.

This was done some time ago, and the packages were all xenial (16.04) and older if I remember correctly (eg. the link you used was from six years ago!). We had no packages in the PPA for bionic or anything more modern, though bionic packages would have been removed as well as we no longer support Lubuntu 18.04 LTS.