I tried on pi 4.
It dosent work
I get following messages:

/home/pi/work/nextcloud/client_theming/client/src/libsync/theme.cpp:34:38: fatal error: /home/pi/work/nextcloud/client_theming/build-1/../nextcloudtheme/nextclo udtheme.h: Datei oder Verzeichnis nicht gefunden
# include INCLUDE_FILE(THEME_INCLUDE)
^
compilation terminated.
make[2]: *** [src/libsync/CMakeFiles/nextcloudsync.dir/build.make:453: src/libsy nc/CMakeFiles/nextcloudsync.dir/theme.cpp.o] Fehler 1
make[1]: *** [CMakeFiles/Makefile2:248: src/libsync/CMakeFiles/nextcloudsync.dir /all] Fehler 2
make: *** [Makefile:152: all] Fehler 2

would be nice to in you can check it
Raspbian version 09/2019
Franz