Just posting as sticky issue for Ubuntu users. The Espresso extension was released as a means to quickly create Gnome 40 compatible version of the Caffeine extension. One tradeoff made to move quickly to Gnome 40 was to NOT build support for any prior Gnome versions. This means that Espresso is not compatible with existing Ubuntu versions up to and including 21.04 because the all use earlier versions of Gnome (ie. 3.38 or earlier).
The good news is that I have been running an Ubuntu 21.10 virtual machine and can verify that Espresso and the Espresso configuration dialog all appear to working correctly with this version.
In the meantime, for your Ubuntu versions up to and including 21.04, I would recommend that you use the Caffeine extension to get the same functionality that Espresso provides.
Just posting as sticky issue for Ubuntu users. The Espresso extension was released as a means to quickly create Gnome 40 compatible version of the Caffeine extension. One tradeoff made to move quickly to Gnome 40 was to NOT build support for any prior Gnome versions. This means that Espresso is not compatible with existing Ubuntu versions up to and including 21.04 because the all use earlier versions of Gnome (ie. 3.38 or earlier).
The good news is that I have been running an Ubuntu 21.10 virtual machine and can verify that Espresso and the Espresso configuration dialog all appear to working correctly with this version.
In the meantime, for your Ubuntu versions up to and including 21.04, I would recommend that you use the Caffeine extension to get the same functionality that Espresso provides.