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 user tip describes what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community.
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 desshoigned solely to seek out adware and known malware and remove it. The free version is more than adequate for most users.
Also, unless you're using a true VPN tunnel, such as between you and your employer's or bank's servers, they are useless from a privacy standpoint: Public VPN's are anything but private.
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.

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.

Copy the report

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

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