Interesting quandary, as LightDM works with other DEs....just not LXQT.  So it's not likely LightDM.  SDDM duplicates the LightDM result....again confirming that it's not likely the DM.  I'm looking squarely at LXQT itself, but you can start it manually from TTY, so that's a head scratcher.   The missing library error message suggests to me that LXQT is somehow corrupted.  Not corrupted enough to prevent starting & using, but corrupted in the interface between the DM and the DE.  Which makes me think that SB is onto something with his systemd comments.  Systemd trying to start a component that isn't there (missing library?) when the DM "hands off" to the DE.  Your manual intervention is bypassing the "handoff", so no issues....you're using the LXQT components as a "skin", but not an LXQT session, if that makes any sense.   At least it's not a mission critical "this must be solved or I can't use the machine" error.  Your workaround is certainly a viable option.  I wonder if re-installing LXQT would solve the issue?  Maybe even force install dependencies with the -f flag?  Just thinking out loud....

Neat but I just subscribe to the news and get an email whenever something is posted   https://lists.archlinux.org/mailman3/lists/arch-announce.lists.archlinux.org/

A very neat way to get important Arch update news !!    I found this neat bash function  whilst conducting Window Maker guerilla promoting at reddit. I installed it  and it works really well an I think it is pretty darn neat an dead simple to implement. Proper KISS stuff. 😋   https://www.reddit.com/r/archlinux/comments/1ljpqf5/comment/mzltvox/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button   For updating, I have an alias in my bashrc that looks something like this:    alias pacu="news; pacaur -Syu"   That "news" command in the alias is a small script that prints Arch latest news. Some parts of that output are brightly colored to make it easy to notice that there's very new news entries.  That "news" command is this function in my .bashrc.   news() { echo $'\e[0;34m:: \e[1;37mArch Linux News:\e[m' perl << 'EOF' use Date::Parse; $_ = qx{curl -s "https://archlinux.org/feeds/news/"};** for (m{<item>(.*?)</item>}sg) { ($t) = m{<title>(.*?)</title>}; ($d) = m{<pubDate>(.*?)</pubDate>}; $t =~ s/&amp;/&/g; $t =~ s/&lt;/</g; $t =~ s/&gt;/>/g; $d = (time - str2time($d)) / (60 * 60 * 24); if ($d < 7.5) { $c = "\e[0;30;41m X \e[1;31;40m"; } elsif ($d < 14.5) { $c = "\e[0;30;43m X \e[1;33;40m"; } else { $c = " "; } print $c, sprintf("%6.1f", $d), " days ago\e[m | ", $t, "\n"; last if ++$n == 5; } EOF }    

I think there is a problem between X, lightdm and Qt because lightdm works fine to log into Xfce but gives an abort-coredump error with LXQt (missing library.) No matter. Works OK with terminal login and startx.

It sounds like you need to troubleshoot lightdm. BTW I am using lightdm and have no issues. I would check the status of the lightdm service and then the systemd logs for lightdm   systemctl status lightdm.service journalctl -u lightdm.service   That should give you an indication of the problem.