iMac 27" 2019 running slow after internet outage

EtreCheckPro is an excellent tool for finding problems.

Download and run the free version of EtreCheckPro, from > https://etrecheck.com/en/index.html

Then post your Report, as per > How to use the Add Text Feature When Post… - Apple Community

+2 on the EtreCheck report, without info all we have is a symptom (it's slow after an Internet outage) Also remember to restart your modem and router, they were also affected by the outage!!!!!!

clear the cached files in library folders and restart the iMac .

And also check the available storage .