One of the better aspects of the OnePlus 5 is that the phone is pretty developer-friendly. There are already a few custom ROMs and kernels available for the device, as well as unofficial builds of TWRP to flash them. Thankfully, TWRP has begun officially supporting the device, so you won't need to use unofficial ports anymore.

OnePlus 5 support is being maintained by Dees_Troy on XDA, and there don't seem to be any bugs with this official release. Since the port is so new, the TWRP app hasn't been updated yet, so you'll need to manually flash the recovery image for now. You can find the download links at the source below.

Source: TWRP