Speed up iMac

Without more information to evaluate. it is not possible to give you a good answer. Was it always slow or has that recently occurred? Was anything done to change something prior to experiencing the slowdown? There can be too many possible reasons to possibly go into here and maybe none would apply. The best answer is to recommend that you download and install the free app EtreChek. Then run it and be sure to enable full disk access. Then respond with the Etrecheck report which you can post below under Additional text. That report provides a comprehensive overview of your computer which we can evaluate and then make some useful suggestions.

Download and run Etrecheck. Be sure to give it Full Disk access before running.

Copy and paste the results into your reply. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

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

Then we can evaluate the report to see if we can determine the cause of the problem.

FWIW, the current version of Ventura is 13.5. Update then test again.