So, I finally got an answer. In my case, the battery was swelling, and my fans were clogged to a degree. Had the battery replaced, the machine cleaned out, and the issue has disappeared entirely.

And the update to Sonoma 14.1 makes no difference. Apple, can we PLEASE get your attention here? This makes my sweet little MBP into a brick, for all purposes.

OMFG! I bought two brand new LG 32" USB C monitors. Great monitors, and for the first two or three days using them, no instances of this. But now, it's BACK, in force. I've reset SMC and NVRAM multiple times, to no avail. If I plug one or both of them in, immediate spin cycle. HELLO, APPLE????? What the hell, guys?

And the parade of MacOS updates with NO fix for this long-standing issue continues. 13.5.1 acts perhaps even worse, spinning out my machine as soon as I connect one monitor. HELLOOOOOOOO, APPLE???????

Charming! I upgraded to 13.3.1, and now it happens WITHOUT an external monitor connected. I've reset the SMC and PRAM, to no avail. Hello, Apple?????

And the long silence from Apple continues. I'm down to using just the notebook, no externals at all, when I normally run two big external monitors. HELLO, APPLE?????

Still suffering from this, as I have been for the last two versions of MacOS. Prior to Monterey, no problem, since then, hideous degradation when using my 27" Apple T-Bolt display, which I prefer to do actual work on. I got on chat with an Apple support tech, he thought it should go away with Ventura, but no dice, sadly. It's making my machine unusable, for all purposes, and it's an i9 with 32GB! Doesn't matter how many cycles you can pull, if the OS eats them. I've loved my Mac gear for the last 15 years, but this is shaking my faith.