With a HiDPI display, most Qt5 applications do not scale at all. Qt Creator in particular does not. This is a little annoying but can be solved by setting an environment variable. For my display, scaling by 2 is slightly too large but it’s better than having no scaling or blurry text.
This will scale Qt applications that support it by a factor of
2. Decimals can be used but then you end up with blurry text which probably is not worth it. After applying this change I noticed a few applications that now scale correctly: Bitcoin Qt and Synergy.