Last month I sung the praises of LibreOffice but lamented the sorry state of their Mac port. Fonts have never been rendered properly on Retina/HiDPI Macs with it, but the 6.4 branch has such blurry text it was practically unusable.
I tried the 18.104.22.168 pre-release and we have pixellated but clear text again.
According to this bug report, the issue was resolved by building with Xcode 11 on macOS Mojave. Thanks Christian Lohmaier!