This iMac has always been slower than I would expect. It works fine for the most part, but applications can be slow to load and there's occasional beachballing. I've attached the EtreCheck report. (Ignore the bit about Time Machine.)
iMac 21.5″ 4K, macOS 11.5
The best antivirus, cleaning app, and overall maintenance app for Mac OS is Mac OS itself. All you need to do with Mac OS to keep it secure and running well is to keep it up-to-date and do periodic (about 1x per week) restarts. Other than that, leave it alone. Adding third party antivirus, cleaning, security and other types of maintenance apps to Mac OS adds no additional level of security. The only thing these apps do is have the opposite affect users want. They make Mac OS slow, unstable, generate odd behavior (much like you are experiencing) and make Mac OS appear buggy.
Please locate the developers uninstall instructions for Symantec and follow to the letter. Then restart in Safe Mode per the directions in Use safe mode to isolate issues with your Mac and then restart normally.
What you need to do is get an external SSD and after uninstalling Symantec and the third party VPN app and then restart in Safe Mode, clone your internal HD to the external SSD and you should should see a pretty dramatic improvement in performance. The external SSD I recommend for you would be a https://eshop.macsales.com/item/OWC/TB3ENVPSX01/.
The best antivirus, cleaning app, and overall maintenance app for Mac OS is Mac OS itself. All you need to do with Mac OS to keep it secure and running well is to keep it up-to-date and do periodic (about 1x per week) restarts. Other than that, leave it alone. Adding third party antivirus, cleaning, security and other types of maintenance apps to Mac OS adds no additional level of security. The only thing these apps do is have the opposite affect users want. They make Mac OS slow, unstable, generate odd behavior (much like you are experiencing) and make Mac OS appear buggy.
Please locate the developers uninstall instructions for Symantec and follow to the letter. Then restart in Safe Mode per the directions in Use safe mode to isolate issues with your Mac and then restart normally.
What you need to do is get an external SSD and after uninstalling Symantec and the third party VPN app and then restart in Safe Mode, clone your internal HD to the external SSD and you should should see a pretty dramatic improvement in performance. The external SSD I recommend for you would be a https://eshop.macsales.com/item/OWC/TB3ENVPSX01/.
Your internal drive should not be your exclusive Time Machine drive, but in theory it could be.
Follow these steps. This will erase all data on the drive, and these steps must be carried out AFTER an external SSD is setup as your startup disk:
Finally, setup Time Machine: Back up your Mac with Time Machine - Apple Support.
Jack
Welcome to the Apple Support Communities.
Delete Symantec.
Other than that, the reason your iMac is very slow is due to the 5400 rpm hard drive. Very slow. If you use an external SSD and run macOS from that, it will make your Mac 10 to 30 times faster for storage. For more info, instructions, and what external SSD to buy, please read: https://discussions.apple.com/docs/DOC-250003583.
Jack
Also, delete any VPNs and other “Privacy” extensions.
Do you have more information about turning the internal drive into a Time Machine backup?
Diagnosing slow iMac
