Thomas Ward has published an update about the future of the Ubuntu MATE project, which did not have a 26.04 release with the other Ubuntu flavors in April:

There is a new team working on Ubuntu MATE who have stepped up to help take over flavor management. They haven't formally introduced themselves yet, but I can safely say that other developers HAVE stepped up for the future of the MATE flavor, despite its prior team lead having stepped down.

[...] Ultimately, this means that they are working to cover the missed items and gaps, and may quite possibly have a 26.10 release in October of 2026, which I believe they most likely are targeting.

This also means that bugs in the MATE environment and in packages they normally would have shipped had they have a 26.04 release are still going to get attention and fixes. So, effectively, nothing has changed. The only difference is that there was no 26.04 installer image released.

For those looking to install a MATE desktop on a "clean" install of Ubuntu 26.04, Ward suggests installing Ubuntu Server and then installing the ubuntu-mate-desktop package.