On a windows system there are certain folders which are user-write-protected. One of which is C:\Program Files which at first glance would seem to be the logical place. If you install X-plane in this folder, however, you will get all sorts of troubles, because you (or an addon-on) may not write to it.
Another bad idea is locating the X-Plane folder as a sub-folder of the special Documents folder – this results in all sorts of confusion with Microsoft OneDrive.
Make it a habit to create the X-Plane 12 folder in a first level sub-directory of the root. In other words, the ideal place for the X-Plane Folder is simply C:\X-Plane 12.
Alternatively anywhere on a secondary drive if you have one installed.
On a different but related topic, in 2025 you should not be installing X-Plane on a mechanical hard drive. The data delivery throughput is just too slow for a CPU or Graphics card capable of running X-Plane 12. Ideally, install X-Plane the fastest M.2 SSD you can afford, or at minimum on a SATA SSD. Hybrid SSHD drives (Mechanical hard drives with an SSD cache) also don’t cut it these days.