Same situation as Jerseygirl0128. Macbook Pro late 2016 model. Critical software update message randomly appeared one day in work when starting it up. Thankfully I had time machine backups and after exhausting all online help, I reinstalled MacOS. Same issue after a reinstall - "a critical software update is required for your Mac". Brought to the Apple Store. To be honest they had no idea what the issue was or how to resolve it. They took it for evening repairs to do a system reinstall. Not sure what they done as it worked temporarily to the point of setting up the mac for the first time, then went down the same route/error after another restart. Because the issue was so intermittent they could only offer a trade in value to buy a new Mac or for me to pay for a logic board replacement. Not great when it's something not evidently wrong with the hardware after their diagnostic tests. If the software/firmware is conflicting with the hardware, then I think it's their duty to at least offer some good will in replacing the part for free, rather than me paying for their mistakes. Thankfully my work have offered to go with the trade in option, but again to their expense and not Apple's.