It looks like baea4d6 made some changes that are backwards incompatible with Qt versions prior to 5.15. Debian Buster (which the wiki says the build should work with) only has Qt 5.11. If I checkout the parent commit it builds fine again.
./qolibri/src/ebook.cpp: In member function 'int EBook::searchQuery(int, const QString&, SearchType)':
./qolibri/src/ebook.cpp:60:50: error: 'SkipEmptyParts' is not a member of 'Qt'
words = query.split(QRegExp("\\s+"), Qt::SkipEmptyParts);
^~~~~~~~~~~~~~
Edit: I just checked the latest ubuntu release (20.04 LTS). It has the same problem, being on Qt 5.12.
It looks like baea4d6 made some changes that are backwards incompatible with Qt versions prior to 5.15. Debian Buster (which the wiki says the build should work with) only has Qt 5.11. If I checkout the parent commit it builds fine again.
Edit: I just checked the latest ubuntu release (20.04 LTS). It has the same problem, being on Qt 5.12.