New iMac unbelievably slow

I have a new 2019 iMac with 8Gb of memory and a HDD (not an SSD). Yes it's the lowest-end 8Gb iMac from last year.

With no apps running, nothing in the apps to start on login, with a new virgin account created yesterday, with the latest MacOS installed, opening system preferences - just opening it - can take over 30 seconds. Every time. With a beachball wait cursor.

This is not just a little slow. This is unbelievably slow. This is slower than my 10 year old MacBook Pro.

I've run every test on it that I can think of. Checked for processes that are using CPU. Checked for free memory.

Does anyone have a clue?

Could it be misconfigured somehow that makes it truly unusable?

Update

If this performance is because of the hard disk then you are saying that Apple is selling a configuration of iMac (in early 2020) that is hopelessly misconfigured. It's as if they were selling a computer with a 128Meg disk or with 1Gig of memory. Can that actually be?

You are on the correct track to make specific benchmarks and time them.

So if you have “open system preferences” you can repeat it. If it takes 30 seconds to open 5 times in a row, you could run some tests to see if it’s network or disk or CPU that’s constraining it.

If it speeds up the second and third times, then it’s a different issue.

Can you reproduce this in a new user account on the Mac with no startup items?

Either way, using the first two Activity Monitor functions to end high CPU use processes and see overall energy use should out any apps causing a slowdown. Also, do you need more ram?