So the culprit is the Nvidia WDDM 2.7 drivers combined with a Windows build of 21H2 or higher (2004 will probably have the issue but didnt confirm).
I will explain how it was diagnosed to help others, but do note I never have actually fixed the problem directly, but at least found the cause.
As reported in the question, I was observing very inflated commit usage vs physical memory usage, and to get anywhere near full RAM usage under normal conditions I would have to enable a very large swap file (42 gigs page file to max out 32 gigs of RAM). As I had approx 2.1 commit to 1.0 RAM ratio.
Shutting down everything in the system tray, all foreground apps did not yield any result. I suspected driver (kernel) related at this point.
Then by accident I noticed something interesting, one day I accidentally triggered a windows shutdown with apps running, I clicked cancel on the prompt for unsaved work, and was back at the desktop with barely anything running, and the commit had dropped by a whopping 20 gigs. I had noticed windows search was no longer functioning.
As it turns out in Windows 1809 (my previous build I upgraded from with no problems), does not GPU accelerate the textinputhost.exe and searchapp.exe whilst 21H2 does. Two system critical windows binaries that are running all the time. The primary culprit in terms of background commit leakage is textinputhost.exe.
If I uninstall my Nvidia GPU drivers the problem goes away, it also goes away if I keep installed but use the integrated Intel GPU for the desktop applications as primary GPU.
If I downgrade to any Nvidia driver version prior to 451.48 the issue goes away albeit with weird desktop performance issues (these issues dont exist on 1809).
Before testing the driver I think WDDM 2.6 might also have been to blame, but Nvidia introduced WDDM 2.7 support in the 45x drivers.
Windows 10 1809 doesnt have the problem but it doesnt GPU accelerate textinput host and also has no WDDM 2.7 support.
So I can recover lots of commit when at high uptime on a whim now by killing those two processes, or I can bypass the problem using my iGPU for the desktop which I am now currently doing, the Nvidia only for games.
Note all Nvidia GPU accelerated apps have the high commit vs physical ram usage problem, so games e.g. have inflated commit values, but as they run for short sessions at a time its a much less severe problem.
I tried a clean install of the OS, and nothing fixes it, as obviously I wanted to rule out if something on my existing install was triggering the problem, but on a brand new clean install the problem still exists, on any WDDM 2.7+ Nvidia driver.
In addition to the bad ratio anything running accelerated on the Nvidia 2.7 drivers would also memory leak over time, a gradual increase of usage, another observation I made that helped me point to drivers, was this leak would reset if I put the PC to sleep and then wake it up again.
For those interested I can post my screenshots, as I made a dozen or so in preparation for posting before I made this discovery.