Attached is the zip file with my Prepar3d v3 add-on.xml file. I guess the legacy models are now gone and P3Dv3 uses the PBR models?
No, P3D3 doesn't support PBR, so the add-on.xml file that is created for P3D3 is supposed to point out to the Addon Manager\Simobjects\Legacy folder, not the PBR folder. An add-on.xml for P3D4 would be correct, if it looked like that.
Do you have both P3D4 and P3D3 installed ? Is it possible your P3D4 registry is pointing to P3D3 ?
Also, note e:\programs in the addons.xml file is not my %ProgramFiles%.
That's not relevant. We install in the folder you said you wanted to use, which by *default* it's your standard Program Files (x86) folder, but that's just a suggestion, you are free to change it anywhere you like so, apparently, when you installed GSX, you asked to install into E:\Programs so is all normal, assuming you did so.