By the way with VLC and the option --sout-keep I can stream (without re-encoding) a collection of videos with the exact same characteristics without glitches.
These are different things. VLC is a client which contains a video player. ETV is a server which generates video and is therefore restricted by the capabilities of the client video players. Opening a single channel and having mixed content (resolution changes, framerate changes, audio channel changes, codec changes, etc) is not something that video players naturally support. While in your scenario, VLC understands that there are multiple items in its playlist. If there were a solution to watch everything seamlessly without transcoding it would be the solution; there would be no need to transcode.
With that said, I have had varying degrees of success with HLS Direct and TiviMate (Android), MPV (Desktop) and Jellyfin (Desktop - not browser).