Something else is going on there. I did that to a friend's laptop that was running epic slow for no reason, about the same age. I never had a chance to get to the bottom of it as it was lost in a fire, but there is something causing a hang-up.

I have a 6 year old 7th gen i5 laptop here with 16GB + SSD in it and it is smooth as butter with stock Windows 10 and about a billion things going on. I have it running two screens and I use it for editing 4K video, doing livestreaming etc. In fact, I have a second identical one with only 8GB in it and it is perfectly fine as long as it doesn't go to swap.

The SSD I put in is a $10 job from Amazon.

I wonder how to get some sort of system-wide profiler that will show where the hang-up is?

I think it has to do with working off of an SD card. My onedrive (with documents, desktop, pictures, video) are file on demand on sd. I am 80% sure that is the case.