I hereby translate the thematically appropriate answer from Volla in the German forum:
viewtopic.php?p=5299#p5299
Thank you for your interest in a Volla tablet. HDMI image and video output via USB is only possible with the USB 3.1 standard and a chipset that enables HDMI output. This is extremely rare with chipsets for mobile devices. In addition to Apple, Qualcomm offers chipsets with this function. With our chipsets from Mediatek, wired output with the DisplayLink protocol via USB-C with USB 2.o is possible. Volla OS supports DisplayLink, possibly also Waydroid on Ubuntu Touch. For Ubuntu Touch we are planning to support Miracast, which is also already available on Volla OS.