I see a number of issues that should be addressed:
1 - first and foremost you should get a full backup of your boot drive either with Time Machine on an external drive or with some other backup app. Not having a backup is like driving without using seatbelts. You don't need them until you do and then it's too late.
2 - 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.
Also, unless you're using a true VPN tunnel, such as between you and your employer's, school's or bank's servers, they aprovide false secutiry from a privacy standpoint. Read these two articles: Public VPN's are anything but private and Former Malware Distributor Kape Technologies Now Owns ExpressVPN, CyberGhost, Private Internet Access, Zenmate, and a Collection of VPN “Review” Websites.
That being said you should uninstall Avast and NordVPN according to the developers instructions. You can check to see if you've removed all of the supporting files by downloading and running the shareware app Find Any File to search for any files with the application's or the developer's name in the file name. For the two software apps mentioned you'd do the following search(es):
1 - Name contains avast
2 - Name contains nordvpn
Any files that are found can be dragged from the search results window to the Desktop or Trash bin in the Dock for deletion.
FAF can search areas that Spotlight can't like invisible folders, system folders and packages.
If you get warnings that the file can't be deleted because it is in use or used by another app boot into Safe Mode according to How to use safe mode on your Mac and delete from there.
Note: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will assure a successful boot into Safe Mode.
Lastly you have way too little free space on your boot drive. That may be the biggest contribution to the Mac's slowness. You should try to maintain a minimum of 80-100GB of free space at all times to facilitate optimal system and application performance.
Get an external SSD, formate it APFS and move Photos and Music libraries to it (make sure they work as expected before deleting from your boot drive). You can create secondary folders for them like Pictures-2 and Music-2 on the external drive and add those folders to the Finder's sidebar for quick access.
You should also backup the external SSD with Time Machine or whatever alternate you decide on. I use both: Time Machine to get versions control, i.e. if I delete a file by accident I can get the latest version via Time Machine. I also have a bootable clone of my boot drive that I update once daily with Carbon Copy Cloner. This lets me boot into it if my internal boot drive ever gets compromised so I can continue working.
