Follow-up
menu-opacity is handled by compton-conf and there is no use for it in picom it was changed.
So, to configure picom we should fork and update compton-conf (c++ and qt skills) or make a new one maybe in pyqt with QSettings.

Some new thoughts about this issue.
I've been using picom delivered in hirsute it work with no problem. But there are a few thing to do be fore a full migration.

Problem appears to be libkf5iconthemes5 5.80. Debian sid has 5.78 now
https://forum.manjaro.org/t/just-did-update-no-icons/58919
https://www.gitmemory.com/issue/lxqt/libqtxdg/246/802661171

Problem appears to be libkf5iconthemes5 5.80. Debian sid has 5.78 now
https://forum.manjaro.org/t/just-did-update-no-icons/58919
https://www.gitmemory.com/issue/lxqt/libqtxdg/246/802661171

Tested LXQt 0.16 on Debian Sid and this problem doesn't happen. Maybe a build problem? I don't think is a configuration issue. Same as T206

Tested LXQt 0.16 on Debian Sid and this problem doesn't happen. Maybe a build problem? I don't think is a configuration issue. Same as T206

tested with kwin instead of openbox and icons are also missing.
Tested with Breeze icons, featherpad icon appear but kcalc does not.

kcalc in 20.10 is version 20.08.1 (with icons), in 21.04 is 20.12.3 (w/o in main titlebar but yes in preferences.)
Featherpad (0.17.1) should be tested with openbox in Debian to see if i'ts lubuntu problem or not.

since LxQt 0.16 the colors can be changed individually, but there is no way for easily create and distribute themes, here is a sxcript we could use as base which added/changed the settings in ~/.config/lxqt/lxqt.conf which handles the colrs

Further investigation needs to be done to see if it's an lxqt problem or not and if it is report bg to lxqt.

found the commit https://phab.lubuntu.me/rSEEDe36f3c2f194882802b1d904983f0edfb1d5a8303
there is a papirus theme, I tried it and didn't like it. https://github.com/PapirusDevelopmentTeam/papirus-libreoffice-theme

I know we did something, that's why we have not the default icon set. It was old task96 before the data loss, we couldn't recover it.

XDG_DATA_DIRS are set in /etc/X11/Xsession.d/60x11-common_xdg_path
https://askubuntu.com/questions/1179729/where-is-xdg-config-dirs-set

with https://phab.lubuntu.me/rDEFAULTSETTINGS15afd8096a302c181c0c2c19e515ee0f5b1dd0eb
the printing problem should be solved. There is some small bug still present that content freeze but a change in window size make it work again.

Puppy minimum requirements are 2Gb Ram and core2duo 64bit.
http://distro.ibiblio.org/puppylinux/puppy-fossa/release-fossapup64-9.5.htm

This is already present in 0.15 which is in 20.10

Upstream has added theming options https://github.com/lxqt/lxqt-config/pull/629 at this stage is less than the hack of use color-schemes.
https://github.com/lxqt/lxqt/issues/572#issuecomment-697865148
But apparently mi idea of using kdeglobals won't work with a new LXQt release.

I added support for menu transparency in my opinion it is ready. but sin it have so much text I'm trying (without success) to internationalize it with gettext, I have .pot and .po files and I'm using dh-translation but I haven't found concrete documentation on how to handle it, I've tried to imitate what software-properties does without success. If someone could guide me it would be nice.

we have the SAL_USE_VCLPLUGIN=qt5 enviroment variable set in lxqt-session.
We don't have the cairo because of the bug mentioned before. https://bugs.documentfoundation.org/show_bug.cgi?id=131625
That bug is fixed in LO 7
However, qt5 VCL might be a little unstable, I had some issues with pivot tables and redraw, but haven't created the bugs for it.
If you are willing to help set both env variables en test with LO 7 and report bugs if you find one/some.

Bumping this task.
adding new insights:
https://blog.lxde.org/2016/10/04/benchmark-memory-usage-lxqt-desktop-environment-vs-xfce/

I think this called picom now

nice addition, thanks

Finally I could solve the test issue, here is the code https://github.com/hmollercl/lubuntu-breeze-config
If we create a phab repo we could add it there.

@tsimonq2 do you have any news on this?