Wireshark 2.6 appears to be the last release

In Summary :

Wireshark, world’s most popular open-source network protocol analyzer, has been updated to a new stable series, versioned 2.6, a major update that adds numerous new features and improvements, as well as support for new protocols.

 

A lot of user interface improvements have been made since Wireshark 2.5, and Wireshark 2.6 appears to be the last release that will support the legacy GTK+ graphical user interface, as the development team announced it wouldn't be supported in the next major series, Wireshark 3.0 .kindly refer the following link as follow up :

https://news.softpedia.com/news/wireshark-world-s-most-popular-network-protocol-analyzer-gets-major-release-520851.shtml