So, in Kubuntu there is a checkbox to add automatically the extension for .docx Why doesn't appear in lubuntu?
https://bugs.launchpad.net/ubuntu/+source/libreoffice/+bug/1812101/+attachment/5230005/+files/Capture%20d%E2%80%99%C3%A9cran%20du%202019-01-17%2017-14-44.png

Olivier replied in upstream bug confirming the issue in 6.2.- https://bugs.documentfoundation.org/show_bug.cgi?id=122752#c4

LO 6.2 has VCL=qt5, which has the extension checkbox but currently doesn't add the extension. Bug filed for that https://bugs.documentfoundation.org/show_bug.cgi?id=123058
Apparently there exist libreoffice-qt5 https://git.launchpad.net/~libreoffice/ubuntu/+source/libreoffice/tree/control.qt5.in

Alright, so from what I can tell, a commit fixing this is now upstream.

@hmollercl Would you like me to work with oSoMoN on this or would you like to work to cherry-pick that commit (referenced in the bug), test it, and then submit it?

My understanding is that upstream fixes doesn't still work.
VCL=kde5 uses kio to put the checkboxes, so not best way to go. Moreover, one of the fixes addedin LO will make VCL=kde5 and gtk3 fallback to qt5 when lxqt is used.

VCL=qt5 is buggie:

• takes more than 10 minutes to start in 6.2 RC3 (https://bugs.documentfoundation.org/show_bug.cgi?id=123072)
• bakcsapce doesn't work in calc
• checkboxes exist but doesn't add the extension (https://bugs.documentfoundation.org/show_bug.cgi?id=123058)

but, we should be ready to run easily in VCL=qt5 (or qt5+cairo according to 10minutes bug) when 6.2 comes to ubuntu, I don't know if we are, maybe oSoMoN (Ollivier Tilloy?) know, I tried to ask via IRC but didn't get a clear answer, only that whe is working on bringing 6.2 to ubuntu, but doesn't know when.