How can I speed up a slow iMac running Sonoma 14.0 for light-duty tasks?

Boy do I dislike it when moderators re-title a thread!

We might be able to help figure out what’s going on with your Mac. It could be anything from an unintentional malware installation to a hardware bottleneck or failure. Some things are fairly easy to fix.

Please run an EtreCheck (free) evaluation of your Mac and post the generated report back here in a reply. EtreCheck is a safe and highly regarded utility from a trusted developer and respected ASC contributor. The diagnostic report will not include any personal info. It simply gathers specifics about hardware performance and installed software that might be in conflict with the OS.

Please navigate to EtreCheck.com to download the utility. Be sure to Allow Full Disk Access when you install the app. Once you’ve run the app and created your report please post it with your reply to this message. 

Please note you must upload the full report. To see how, please click >  How to use Add Text when posting… EtreCheck Report.

We’ll use your EtreCheck report to look for the things that may be causing your problem and advise how to correct them.

This: What to do before you sell, give away, trade in, or recycle your Mac - Apple Support

It’s kind of the scorched-earth approach. It’ll wipe everything and let you start over as if you’d just unboxed the thing.

I didn’t see original question, but to respond to current title:

Is this a 2019 with a 1TB HDD?

If so you need to purchase an external USB-C SSD and reinstall MacOS onto that. (HDDs are too slow for Sonoma). Install macOS on an external storage device and use it as a startup disk - Apple Support

If you already have an SSD, run Etrecheck and post the results using the “additional text” posting option.

D.I. Johnson wrote:

Boy do I dislike it when moderators re-title a thread!

Agreed, the re-title has nothing to do with the OP's original question.

padams35 wrote:

I didn’t see original question, but to respond to current title:

I don't have a screenshot of the original question to push the issue, but it went something like this:

How to erase and reinstall a slow 2019 iMac to use as a music player and searching the internet?

It was retitled after both D.I. Johnson and I replied.

see > Use Disk Utility to erase an Intel-based Mac - Apple Support

and then > How to reinstall macOS - Apple Support