2020 Macbook Pro Sequoia 15.6 runs when lid is closed

Are you using?

• An external display, try turning off the display before the lid is closed.
• Wired External keyboard and mouse, try using Bluetooth Keyboard and Mouse, preferably Apple devices. Mice & Keyboards - Mac Accessories

<< I will put the Macbook Pro (2020 Intel, two ports) to sleep using the Apple menu, close the lid, ... >>

I suggest you try NOT choosing sleep, but ONLY use the lid-closing as the ONE signal for your Mac to sleep.

The reason I say that is, it is possible the lid-closing on an already-sleeping MacBook Pro might cause an interrupt, (indistinguishable frorm a lid-opening event) that would wake it up instantly.

You could confirm that yourself by opening the display an extremely small amount, enough to see if the display is lit up, but not enough so that it would actually wake if it were sleeping.

<< I ran Activity Monitor and the CPU cycles were almost entirely in kernel. The CPU % of kernel_task was over 1300% (no typo, not sure how it does that). >>

that number show 100 percent when you are using 100 percent of the compute power of ONE CPU.

When your Mac gets HOT, Kernel-task grabs additional time slices and runs a cool-down loop, built of very simple machine instructions that use very little extended power.