.ini configparser worked fine for decades, especially as a simple project config.
Toml is ill-defined as well. ini files work fine for these trivial uses.
https://hitchdev.com/strictyaml/why-not/toml/
So now you have two flawed ways to do it, congrats.
Python 2 is EOL, so that's no longer a concern.
As for differences between Python 3 releases, isn't there a fairly large difference in TOML support as well, since in versions before 3.11 it doesn't work at all? Wouldn't specifying the behaviour of the INI parser as whatever 3.11 is doing (and raising an exception on earlier versions) amount to essentially the same thing?
However you prefer to work, your tools may now be easier to test and maintain. This change is good for everyone.
Otherwise, adding tools to the standard library to read file formats required by the ecosystem is a good idea, regardless of whether you agree with the particular format.
History has shown that worrying about an incompatibility with the moribund Python 2 that never affected trivial packaging config was a waste of time.
Meanwhile we still have a setup.cfg on a work project, has worked without issue for 15+ years.
We have a 15 year old setup.cfg in one project at work, many other .ini's... has never been an issue.