So on one hand you're lagging 4 years (and 4 versions) behind, but on the other hand it's just 4 years and 4 versions. I like your approach. Without it there'd be no progress. Google has similar policy in many places.
It is the standard policy in the Python ecosystem, keeping in lock-step with the Python support schedule (see e.g. https://endoflife.date/python ). Although many packages chose to maintain support for Python 2.7 well into 2021.