There are two major benefits in ergonomics with fully-splits. They are that, 1, they acknowledge that one size does not fit all in that they offer a way to move them around and find the right angles and positions for you and your hands; and, 2, "the best posture is the best posture" - i.e. the ability to move and adjust your setup throughout the day/session is itself an ergonomic benefit, staying in one posture is one of the roots of RSI.
Another thing that full splits offer that you may find beneficial is tenting, especially (again) adjustable tenting. Monoblocks don't tend to be tented and when they are they are stuck at a fixed angle, if that's not the right angle for you then it's a problem, and adjustability is king for the aforementioned reasons.
Now, there are many factors, split keyboards are not a panacea. Mouses/pointing devices play a role, as do chairs, desks and maybe most importantly habits! Take regular breaks, move around, etc. Again, the best posture is the next posture.
Also don't listen to people on the Internet and consult a doctor/physiotherapist.
As others said, you're talking about CGI