MacBook late 2016 does not recognize internal SSD. I can boot up from an external SSD that has macOS installed
first you should go into macOS Recovery and go to Disk Utility. Select Macintosh HD and then Info. See if the disk is listed as bootable by Disk Utility. If it doesn't say bootable, then try running first aid. If the Disk is not recognized, then see if it is recognized when booting macOS Sierra from the external drive. By doesn't boot up, if you mean it is stuck on the Apple logo, then you can try resetting the SMC and NVRAM/PRAM. Also, try using power-on self diagnostic (you must disable Firmware Password). If none of those work, then try using Single user mode (reboot then Command + S). After that, run fsck_apfs. I am aware that this probably won't work if the MBP won't boot but if you can access macOS Recovery, then you can rest assured that this is not an issue with your SSD being dead. Good luck!