We were able to see this functionality experimentally before, but it has now officially confirmed from Google.
As we can see in Tweet, Danny Sullivan does not recommend expanding content in Meta Description, saying that the snippet content is a much more dynamic activity. In other words, if Google displays a longer label is a matter of the algorithm and not a rule. This is confirmed by the results from the mobile, where the length of the label in the SERP is rather 190 characters.
An important thing I would like to mention is that this change does not mean that Google changes the length of Meta Description. Just that he can write more text into the snippet under some conditions.