Mail timing out/wont connect to iTunes Store/can’t update macOS

You have some adware installed, please download the free version of Malwarebytes and run it. Then restart in Safe Mode per the directions in Safe Mode Reset instructions and then restart normally and test.

Please navigate to the Mac App Store or 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 https://discussions.apple.com/docs/DOC-250000211

Besides the good advice so far, after removing the Adware...

System Preferences>Network>choose interface>Advanced>Proxies Tab, make sure none are set, like for HTTP & HTTPS.

System Preferences>Network, unlock the lock if need be, highlight the Interface you use to connect to Internet, click on the advanced button, click on the DNS tab, click on the little plus icon, then add these numbers...

8.8.8.8

8.8.4.4

1.1.1.1

9.9.9.9

Apply.

I'd also uninstall Memory Cleaner.

Delete these files & restart...

/Library/LaunchDaemons/com.attotech.iscsid.plist

~/Library/LaunchAgents/com.aviatainc.powerengage.helper.FUJ1.plist

~/Library/LaunchAgents/ProtonMail Bridge.plist

These last 2 are hidden...

~ tilde indicates hidden Home Library.

Apple hid the Users' Library folders...

Method 1:

1. From the Finder, select the Go menu at top of the screen, and choose Go to Folder.
2. In the window that opens, enter ~/Library, and click Go.