Since the Creator's Update, not since AU. I advise you not to use this feature though, unless security is your #1 concern. The internal 'drive' can be easily encrypted as it uses a hardware encryption system. This is immediate and uses no CPU resources. If you encrypt the SD card however, it is using software encryption which will be much slower and will lean on the CPU constantly. If you do use SD card encryption don't expect apps or maps to work well from the SD card so put them all on internal storage. Also, record any high res video to internal storage to avoid issues.