Clean HDMI output, is not a feature to decide on while buying a camera
(most of the time)
not all camera's allow you to record internaly, while using the HDMI to output to an external device,
most MFT or DSLR will need a dummy battery for external power, most other camera's will have an external power connection.
I guess one should watch for "mark ?" type of camera for added features, would be nice if a firmware update could add a "clean hdmi" option, maybe start a ticket at such a manufactor, asking for this option....
btw. (random) Youtube tutorials are not complete most of the time, you need to do research for yourself if the sugested options are available on your equipment, or check before buying the equipment, also, do not put faith in the random Youtube guides, there are some good reputable channels, where you also get answers to your questions.