My iMac 2019 with macOS Sonoma is extremely slow

I suspect you have a 21.5" 2019 iMac which has a 5400 RPM HD installed. The HD is the primary bottleneck to these computers as they are glacially slow. However, please do the following.

It will help us get a good idea of what is causing your problem if you provide a report of your system, that way we do not have to play 20 questions with you. The report we are requesting does NOT provide any personal information and is extremely safe to use. Please navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again. 

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click How to use the Add Text Feature When Post… - Apple Community It is helpful to us if you download the report to your Desktop.

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?

Please run as requested Etrecheck and post the results as follows:

Copy the report

and use the Additional Text button to paste the report in your reply.

Then we can examine the report and see if we can determine the cause of the problem.

Another thing you can try if suspect the HD is failing is to download the free (evaluation version) of DriveDX and have it run a report on the HD. If your 27" (there is no such thing as a 27.5") has a Fusion Drive please only run the report on the HD and not the Fusion Drive or the SSD. If the report on the HD indicates ANY errors or performance issues then your hunch is correct and the HD is failing.

A 2019 (hard to believe it's 5 years old already) can be fixed, what most users do if the HD is (or has failed) failing is to buy an external SSD and use the following to setup the external SSD as the boot drive. How to setup an external SSD as your startup disk. The external SSD I'd recommend that you use if you decide to take this route is the OWC Envoy Pro EX Thunderbolt 3