Excellent article.
I do not have the same technical depth to dig this far as the author, but this kind of problem seems pretty common on laptops, especially those with "switchable" iGPU/dGPU setups.
I had an Acer laptop about 7-8 years ago with almost the exact same latency symptoms. In the end I just disabled the dGPU in the BIOS (since I only used it for office work), and that instantly solved the issue.
This kind of thing is very infuriating because not only is it hard to track down the root cause (which I am very grateful the author did), but it is also even harder to get the vendor to actually acknowledge or fix it.
Intel laptops with igpu and Nvidia chips and thunderbolt docks are absolutely a nightmare between the 3 trips video has to go to even leave the laptop and the drivers and firmware mismatches.
I've had weird issues with this setup since the core2duo days upgrading once a year.
when it works it's amazing, however.
AMD igpu and dgpu work super well together but I feel like over time, since I use this configuration the most things either improve or go to hell with driver updates. depends on the laptop OEM really.
This all said, where the hell are the strix points igpus where they rival desktop cards (yes the lower mid end) at laptops where stuff just works without compromise ...if there is power and cooling.
Side note - I have a rog g14 that until I loaded a beta bios for thunderbolt over usb4 would reboot when shut down and shut down randomly. (amd CPU and GPU)