Very slow iMac 2019

First I have asked the moderator to remove the SN info on your computer. Please NEVER EVER post personal information such as SN, Phone Numbers, E-Mail addresses, Physical addresses etc on a public forum.

Now onto your problem. You have a base model 21.5" iMac which has a glacially slow 5400 RPM HD. The RAM is low however 8GB should be fine for most basic computing tasks. There is nothing that will make this computer fast unless you remove the HD from the equation. The simplest way to do that though is to replace that HD with an external SSD. This will dramatically improve performance. However, considering the computer is 4 years old, almost 5 now you may want to consider replacing it with a new 24" iMac or even a current model Mac mini. These new machines are much much faster than what you have and will be quicker than your machine with an external SSD by a bit.

However if you want to put money into it, I get it. Please just follow the instructions in How to setup an external SSD as your startup disk and the speed will be improved dramatically.

This iMac has 8 GB of memory. That’s low.

If this is a hard disk drive iMac with 8 GB (and this HDD with 8 GB is a fairly common iMac configuration), it’ll be slow.

… Why is my hard disk drive iMac so slow? - Apple Community

Migrating to and booting from an external SSD is the usual response, and there’s a link to doing that there.

Replacing the internal hard disk with an SSD and increasing the memory while the iMac is open is far more work, and is much more expense.

Image of configuration reposted, with expurgations: