This morning I had 16" 2019 Intel MacBook Pro with a perfectly fine TouchBar. I updated to Sonoma a few hours ago and since then have not been able to get the TouchBar to light up. It does work, as I can kinda guess where the icons should be and adjust the Mac's brightness and volume, but the TouchBar remains pitch black. I also tried the SMC reset, the PRAM reset and the Kill commands in the terminal, but nothing has worked.
So no, I believe it is not a hardware issue, cause it was perfectly fine just before updating the OS.
Perhaps there are not enough users with this issue for Apple to take notice, which makes me wonder if it is either a "chance" or lottery thing during Sonoma's installation process, or a rare combination of factors that only a small group of users share, or if indeed this is affecting all TouchBar users under Sonoma but only a few are posting about it. If that were the case, it is a major fail that a heavily touted functionality like the TouchBar is crippled by an OS update that remains unfixed as long as it has.