This same problem is on another distro with LXQt and SDDM package. I checked this with Fedora 34 LXQt Spin and I have identical issue. So this is not only problem with Lubuntu.
This same problem is on another distro with LXQt and SDDM package. I checked this with Fedora 34 LXQt Spin and I have identical issue. So this is not only problem with Lubuntu.