These issues are mostly caused by network errors occuring when the plugin’s installation process tries to download the required software packages.
Especially on Pi4 models these errors are often caused by incorrectly set system time/date. So, at first check date and time of your Volumio system. For correcting them see Waveshare 7" hdmi lcd (B) touch screen problem - #15 by Wheaten
Another reason can be unreachable repositories, e.g. because of DNS blocking. Sometimes changing the repository mirror as described here helps.