Howdy!
It can be ANY path you want.
The packages files don’t care where it’s placed, as long as you can tell the MSFS Installer where it is.
I took my existing Packages folder, copied it to a new drive that the PC automatically named as E: when I added the SSD hard drive internally. See below. Note - C: is my dedicated Windows OS drive, nothing else lives there.
Literally, my installation for the Packages is E:\MSFS. Open that folder - you’ll see the two folders - Official and Community.
When the MSFS Installer screen with the infamous blue bar at the bottom loads and it asks where to install the sim, I click into that path box on the lower right and type in E:\MSFS. It takes a couple of seconds for the installer to recognize the Packages are already in there, and starts chugging away.
Also - try to keep it as high as possible in the folder tree. The deeper you put the Packages file - i.e., your example of “E:\Users\MyUsername\AppData\Roaming\Microsoft Flight Simulator\Packages” - the more likely you will run into a “Too long a directory path/file name” error over time. Windows still has a limit to how deep a file can be in order to read it, and if it’s a file with a long name, it’s a double whammy.