Can I reset my 2019 iMac to factory settings for improve performance?

+1 on providing an EtreCheck report. Mac OS is not like MS Windows that needs to be removed and re-added periodically. It is rare when that is required. Your problem may be due to something you have installed and the EtreCheck report will let us know that. Your problem may also be due to a hardware failure (your computer likely is using a Fusion Drive and they can have problems at this age) again, the report may show us hints.

Remember EtreCheck is 100% safe and does NOT provide any personal information about you or the computer.

Before you go to that much trouble, I'd recommend that you download and run the free version of EtreCheckPro, from > https://etrecheck.com/en/index.html

Then post that report in this thread using these instructions:  How to use the Add Text Feature When Post… - Apple Community

Someone then may be able to spot something and be able to make a suggestion that would keep you from having to start from scratch.

Regards.

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac? The Etrecheck report should show us if they've been installed and any other anomalies in the system.