What is HDMI splitter?

In plain language

One source in, two or more identical outputs. Useful for a second screen in another room, or for feeding a display and a capture device at once.

Why it matters in your setup

The source can only receive one EDID, but there are now several displays. Most splitters solve this by taking the lowest common denominator: if one output is a 4K120 HDR television and the other is an old 1080p monitor, the source is told 1080p.

That is the classic splitter downgrade, and it surprises people because the good display was working fine until the second one was connected.

HDCP adds a second constraint: every output must support the version the content demands, so one older display in the group can block protected content on all of them.

What the DR HDMI 8K does with it

A DR HDMI 8K between the source and the splitter lets you decide what the source is told, rather than accepting the splitter's lowest common denominator. Advertise the capabilities of the display you actually care about — bearing in mind that the other screen then has to cope with a signal it may not fully support.