This release adds support for Python 3.10.
It also clarifies the supported versions of Python (following NEP29, any minor version released within the 42 months prior to a pgfutils release) and Matplotlib (any minor version released within the 24 months prior to a pgfutils release). This is currently Python 3.7 to 3.10 and Matplotlib 3.1 to 3.5. The latest point release of these minor versions are used for continuous integration testing.
As a result of this, an obsolete workaround for setting the preamble in older versions of Matplotlib has been removed as it was incompatible with the latest release.