Hi,
I also had noticed this change in the past few days…
When I you do a site: search from my desktop, I see that either the meta description is truncated to fit the new limit, or Google finds something else altogether on the page to show in the search snippet.
Yet, when I press F12 to open Developer Tools (on Chrome, at least), and click on the toggle to see the results as if from a mobile device, (and reload the search to make Google generate a mobile search results page), I see that a larger size applies!
Yet, when I perform the exact same search on my iPhone SE (4″ display), I see that the results are even smaller than what’s being shown to the desktop user.
So I guess if your website is responsive and the same content is served to both desktop and mobile users, you’d have to develop the art of meta description writing to the point that it gives the user all it needs to know in the first half, then add something else for the mobile crowd, hoping that Google finds the room to display it.
This article gives some information about the move toward a dynamically-sized snippet, including quotes from Google about it:
https://www.compose.agency/insights/meta-description-length-2018