I would stay away from all anti-virus apps except for MalwareBytes since all the other anti-virus products tend to install dozens of drivers & startup items which makes them much more likely to interfere with the normal operation of macOS. No, stay away from Avast! They have already been caught at least two different times selling personal information, and these forums are full of users reporting major system issues when Avast is installed. You may also want to run the Apple Diagnostics to see if any hardware issues are detected. If Safe Mode works fine, then you likely have an issue with some third party software or a login item. See if you have the same issues while booted into Safe Mode which disables third party Startup & Login items. If you give EtreCheck 'Full Disk Access', then the report will include more information including a summary of recent logs which may contain clues.

To look for possible software issues you can also run EtreCheck and post the report here using the 'Additional Text' icon which looks like a piece of paper. FYI, MalwareBytes has an 'uninstall' option which can be found on one of the app's menus IIRC.

MalwareBytes is the only exception to the rule. Stay away from all other anti-virus apps, cleaning apps, and third party security software since they usually cause more problems than they solve since they interfere with the normal operation of macOS. You can use MalwareBytes to scan your Mac if you believed you may have been infected with malware or adware, but there is no reason to keep it installed.

Malwarebytes is it good