I have seen differences in displayed window behavior between using Sierra and using High Sierra as the OS. Last I had seen displayed windows were not working at all for Sierra (exactly the error messages Olivier has shown), but were working fine (except for a warning message with each new window) for High Sierra. This issue is either in the Qt package or the OS. Possibly updating to the latest Qt/PyQt (if not there already) may help.
I do not recommend using the prebuilt distribution for Mac; I probably will not provide that package in the future. Instead, as Ryo mentions, use the conda build or build it yourself using Homebrew packages.
Kind regards,
Karl