How to fix a slow iMac

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1

After upgrading to macOS Big Sur my internet speed came down from 430 Mbps (download) to 25.9 Mbps.
Programs load very slow, constantly I get the round colored little ball before I can access a program, not being able to type before waiting to see what I typed and my work slowed down to hours instead minutes.

Norton 360 Multi-Device

S/N:   T4VQYB34RRH3

macOS Big Sur,  Version 11.1

Mac (Retina 5K, 27-inch, Late 2015)

Processor  3.3 GHz Quad-Core Intel Core i5

Memory  8 GB 1867 MHz DDR3

Graphics   AMD Radeon R9 M395 2 GB


I Uninstalled Norton 360 and had difficulty to use the clean all Norton files.
After reinstallation the situation did not change.

Is there an incompatibility between Big Sur and Norton 360?

How can I get the computer to work normal again?

2

Good luck, I have been complaining about this issue for some time without resolution.  

Check other topics.