I'm not sure if this is the expected behavior but setting license = {file="COPYING"} and "License :: OSI Approved :: GNU General Public License v3 (GPLv3)" doesn't work as expected for example with flit:
https://github.com/SciQLop/PyISTP/blob/main/pyproject.toml
I get on PyPi:

While with mesonpy:
https://github.com/SciQLop/CDFpp/blob/main/pyproject.toml
I get on PyPi:

BTW you get the same on PyPi:

This seems more related to mesonpy than PyPi I think.