Uninstalling Apple bloat ware

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 AVG 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. 

Download and run Etrecheck. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and use the Additional Text button to include the report in your reply.

IMPORTANT:

Before running Etrecheck assign Full Disk Access to Etrecheck in the Etrecheck's Privacy preference pane so that it can get additional information from the Console and log files for the report:

Also click and read the About info to further permit full disk access.

Then we can examine the report and see if we can determine what might be causing the problem.

I will offer some thoughts for your consideration. First, removing those apps should not have any effect on the speed of your computer. And some apps can not be removed as they are installed as part of the operating system. You certainly have plenty of RAM, so that is not the problem. I would first confirm that your Mac is "seeing" and using all of the RAM. Open About This Mac, located under the Apple logo. Then click on the Memory button to confirm your RAM is being used. If not, then try reseating it or replacing it. You can swap the modules to see which one is defective (if one is). Next, I would recommend downloading ,installing and running the free app EtreCheck. Be sure to enable full disk access. Then save and post the report it creates below under "Additional text". This report provides a comprehensive overview of your OS. Very likely it will show what is causing your slowness. Then someone here can offer their observations. Do you have any antivirus apps or Mac cleaner apps installed? If so, that will be your problem and they should be removed as they are completely unnecessary. Once it is determined what is happening, then it can be fixed.

I'm running a similar 2020 27" iMac with the 5700XT, 40GB of RAM and I'm not experiencing any slow down. Ronasara is correct the "Apple bloat ware" you are referring to will not be slowing down your computer as none of it has processing in the background. Download Etrecheck and post your results. A couple of questions as well, how much free disk space do you have on this computer? Also is all the software you have one the computer the most recent versions and/or compatible with Big Sur?

Paul

You can keep the AVG in the Windows boot section. It's just not needed on the Mac side.