I just got the Raspberry 7’’ touchscreen running.
I’m almost certain that the following tip can also be found here in community, but so be it…
By installing the touchscreen plugin, I achieved my goal very quickly in my second attempt ;-).
After I downloaded the latest version of the Volumio image (3.611), I created a user userconfig.txt and “called” the following overlay:
The Readme contains the following 2 notes:
The dedictated cables for SDA and SCL are only required for old Model A/B boards where the DSI connector does not have I2C connections. With your Pi 3B+ SDA and SCL signals are already transmitted via the DSI ribbon cable. The cables for SDA and SCL should then not be used.
I think that’s a misunderstanding. The note is related to Volumio images that already provide an option to display Volumio’s UI on a locally connected display on Volumio’s system settings page. IIRC that option is in the section “Video Output Options” and called “User Interface Via HDMI” but is currently not available on Pi based Volumio systems (so you would not find it on your system ) - hence the need for the Touch Display plugin on such systems.
tl:dr Using the overlay “hdmi” should not be required.