After updating my iMac to macOS - Sonoma 14.0

This may be due to something you have installed on the computer. In order for us to get an idea of what be causing your problem we need to have additional information from you. Please do the following:

It will help us get a good idea of what is causing your problem if you provide a report of your system, that way we do not have to play 20 questions with you. The report we are requesting does NOT provide any personal information and is extremely safe to use. Please navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again. 

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click How to use the Add Text Feature When Post… - Apple Community It is helpful to us if you download the report to your Desktop.

No you do not have to keep do that. What you need to do, is uninstall Avast as per the developers instruction.

Avast (and other AV apps) are not necessary for Mac OS. The below types of apps do nothing to help Mac OS be more secure or run better. If you have any of the following types of apps installed, please locate the developers uninstall instructions and please uninstall.

·      Antivirus Apps

·      Cleaning Apps

·      Security Apps

·      VPN Apps

·      Maintenance Apps

These apps have the exact opposite effects that users want. They make Mac OS slow, unstable, makes it do weird things (the weird things vary from circumstance to circumstance) and do absolutely NOTHING that Mac OS already does. In order to keep Mac OS secure, stable and trouble-free simply keep it up-to-date and restart your computer about 1x per week. Other than that just leave it alone and enjoy it.

Avast is no longer considered a helpful app?

First, there is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus, VPN or security apps on your Mac.  This documents describe what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community and Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support.  

There are no known viruses, i.e. self propagating, for Macs.  There are, however, adware and malware which require the user to install although unwittingly most of the time thru sneaky links, etc.   

Anti Virus developers try to group all types as viruses into their ad campaigns of fear.  They do a poor job of the detecting and isolating the adware and malware.  Since there are no viruses these apps use up a lot of system resources searching for what is non-existent and adversely affect system and app performance.

There is one app, Malwarebytes, which was developed by a long time contributor to these forums and a highly respected member of the computer security community, that is designed solely to seek out adware and known malware and remove it.  The free version is more than adequate for most users.  

Unless you're using a true VPN tunnel, such as between you and your employer's, school's or bank's servers, they provide false security from a privacy standpoint. 

Just some more food for thought.

Avast nags me everyday about allowing it to access data from other apps on my iMac. Do I have to do this?

No it is not.

see > macOS - Security - Apple