Windows Mobile 6.5 (WM6.5) was released in 2009 as a bridge between the legacy Windows Mobile era and the newer Windows Phone 7. Because of its age and "End of Life" status in 2020, obtaining a standard ".ISO" file like you would for a desktop OS is less common than finding device-specific "ROM" files.
Windows CE End of Life What It Means and Your Upgrade Options
But for pure nostalgia? Nothing beats the real thing.
Rarely. Unless you are maintaining a legacy warehouse scanner (many old industrial PDAs run Windows CE/6.5), there is no practical reason to boot it.