I'm unclear what the statement should communicate. Is it intended as a general description to give context what mathtext is? That'd be a bit odd. We don't have such descriptions for other what's new sections.
Or does it document the improvement in this PR? In that case I suggest

I think here @jklymak is specifically adding the context. In the issue it's supposed to be closing #26968, the issue poster was trying to use a mathtext feature while also setting usetex as true.

Granted, we could also be probably be more direct "These features are additions to :ref:Mathtext <mathtext> and may not work if :ref:usetex<usetex is set to True" since this is a what's new.

"mathtext" is jargon, so it would be nice to define it, at least by a link. None of the code provided helps with the context either, since it could easily apply to usetex labels.

Ah, I see, this is an intro paragraph to a set of changes. While we typically don’t have that, I acknowledge your point on giving context. I’m +/-0 on this. Fundamentally, we can’t explain every concept of the library again in the changelog (e.g. we also don’t explain what a formatter is even though not all users will be familiar with that concept).
I’d be in favor of only linking, but not explaining. - Possibly even just link the “mathtext” word in the individual improvement messages.

But I withdraw from the discussion now. I’ve added my view and leave it up to you to decide this topic.

I don't believe just putting a link in would have helped the OP (why would you click a link for something you think you understand) and folks are often confused by the difference between usetex and mathtext; there is a whole community that always have usetex=True, and probably forget that Matplotlib has mathtext handling. I don't think it hurts to explicitly remind them here.

I changed this sentence to be:

Improvements are to Mathtext, Matplotlib's native TeX-like mathematics parser
(see :ref:`mathtext`, not to be confused with Matplotlib using LaTeX directly:
:ref:`usetex`).

It seems you haven’t pushed yet.

ooops....