HDMI does support DPMS. It just that TVs don't. I doubt well every see a display port connector on a TV and/or DPMS support because that would rob them of being able to have an almost identical product that is only a slightly tweaked TV that is little to no cost to them that they can charge charge a whole lot more for.I'm a bit more surprised HDMI still this day doesn't support DPMS-type functions to some extent, even if "legacy" vs. only CEC. Likewise I'm surprised companies like samsung don't just include a DP port on their TV's...
I figure at some point a developer might buy a few of these tv's and realize how asinine this all is to use to resolve it, but considering here we are in 2020 and my first reports of some of this stuff began a decade or more ago, perhaps not. KDE is still working on trying to fix window placement a decade or two on, seeing this just today...