tried the dism way? adding .net 4.8 on same LTSB(1607) x64
Code:
dism /online /Add-Package /PackagePath:windows10.0-kb4486129-x64.cab
what error you get? whenever I couldn't add a new package to windows was because I did it on a ntlited (or similar) install that was missing some (removed) things...
or as FoxB suggested, just use the netcore package