Created attachment 166651 [details]
example file showing intended tree lines
Tree views for non gtk3 actually do display lines but are immediately painted over by the entries. I noticed this while investigating bug 136962 on my not so powerful newly set-up windows LO development computer :-)
Attachment 'non_gtk3_treeview_with_lines_examples.odt' shows Windows platform lines vs no lines differences and Linux X11 and KF5 examples with lines.
Link to patch that makes the lines show:
Arch Linux 64-bit
Build ID: 496771a6466d6a48f0bcbd8976df24308e052f38
CPU threads: 8; OS: Linux 5.9; UI render: default; VCL: kf5
Locale: fi-FI (fi_FI.UTF-8); UI: en-US
Built on 28 October 2020
Jim Raykowski committed a patch related to this issue.
It has been pushed to "master":
tdf#137693 fix sal tree net line rendering
It will be available in 7.1.0.
The patch should be included in the daily builds available at
https://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More
information about daily builds can be found at:
Affected users are encouraged to test the fix and report feedback.