The above procedure had returned the Volumio UI to the HDMI screen. The LCD screen remains white.
My display is this one
3.5 Inch Touchscreen HD Touch Screen W/ Cooling Fan And Case For Raspberry Pi 4B | eBay
Tomorrow I will open the case, extract the display PCB and send you pictures of it.
Meanwhile, I find no words to thank you for the prompt support.
Will contact you tomorrow