Hi, @lihuto
The latest available version of the "Ubuntu MATE" Linux distribution is "Ubuntu MATE 24.10" ("Oracular Oriole") - which uses the version 1.26.2 of the "MATE Desktop Environment". I've just created an "Ubuntu MATE 24.10" VM in my computer and the "Test Speakers" button is available in that "Hardware" tab of the "Sound Preferences" window. Here's a screenshot:
