This happened with my 2019 16" MBP (i9 8-core 2.3GHz). No charger, including Apple's own 96W, was enough when doing something heavy like CPU video encoding.
Last year I had to convert some blu-ray movies so I could stream them to my TV and it was common to go to bed with 100% and wake up at 20% or so. Throttling kicks in when the battery is too low, so I don't think it would shut down, but yeah, this was one of its flaws.
It also overheats and throttles very quickly (~1 minute) even with a more aggressive fan curve or even fans manually set to run at 100%. This can be managed by disabling Intel's Turbo Boost or by using Monterey's power saving mode, but that's not something one expects to do on a "Pro" machine.
While I don't agree with parent's declaration of all MacBooks being toys, that battery drain issue while being plugged in definitely did happen. Couldn't find a source for it just now, though. It used to happen on my 15" 2013 MacBook Pro when it was plugged in and I was playing games (BioShock Infinite was one such game).
It is easy to make my 2019 16" MBP consume more than the 96W that the included charger provides. Loading the CPU alone gets you close to that. Just add some discrete GPU work and there you go.
In fact, since connecting an external display enables the dGPU, the consumption can increase enough to get you over 96W with the CPU alone
Nope. The charger provided with 16" MBP (2019) can't delived the maximum required wattage to the MBP if everything (CPU, GPU, screen brightness) is at max usage. It's no issue for "everyday use" of most users, for sure, but for a pro machine...
I almost had this happen on my M1 MacBook Air yesterday. I used the included charger on my M1 MacBook Air a few days ago. I was watching The Witcher Season 2 HEVC 4K HDR (so the highest quality) on it and had Cura (3D printing software) on in the background. I had the notification “MacBook is not charging”, since it was using power too fast apparently.
Not sure if it was draining but the battery wasn’t charging either. I closed Cura and it resolved the issue though, I went from 90% battery to 10% in about 2 hours though before plugging the laptop in.
I've only ever seen this happen if you use the lower wattage charger from a 12" Macbook Air with a higher spec'd Macbook Pro.