OP here...The Saga continues. So I see at HD that the Sharkbite (SB) brand has expanded. So heres the specific SB - push to connect - I know works and the packaging states use with PEX:

using those SB PTC above will eliminate having these god awful pinch clamps (which somehow are now branded as SB!):

So I managed to replace the "T" and 90 elbow to be leak free, thusly:

but if course, all that yanking and pulling and flexing the manifold to get that done cracked yet 2 more of the original black plastic fittings, which now leak. So I committed now to replace all the fittings in this assembly. I managed to find all the valves and other fittings in SB PTC EXCEPT the 2 "hose" connection 90 elbows to the WH tank:


I cannot find, even on the SB website, a 3/4 inch female thread to 1/2 inch SB PTC.
I see it in 1/4 inch on Amazon looks like these:


So if yall fine gents/ladies ever run into this and located such a fitting let me know. I imagine I could get this done through multiple adapters or the SB water heater hose connection for 1/2 inch but thats not preferable.