Big Sur Upgrade Slowed Down MacBook Pro

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.  

That being said you should uninstall ProTec6 according to the developer's 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 ProTec6 software you'd do the following search(es): 

1 - Name contains protec6

Any files that are found can be dragged from the search results window to the Desktop or Trash bin in the Dock for deletion. If you find that you can't delete them because the are in use boot into Safe Mode and do the search and deletion from there.

FAF can search areas that Spotlight can't like invisible folders, system folders and packages.  

Also the Adobe apps are using up a lot of the CPU resources. So when using the Adobe software keep the other open apps to a minimum.

Don't let your free space get any smaller. Actually if you can free up 80-100 GB of free space that would definitely help in performance.

Note: you can empty the Downloads folder after the apps and/or updates that were downloaded have been installed or applied.  Many users have found a couple of Gigabytes of files in their Downloads folder which are no longer needed. 

This Mac looks well and truly stuffed with apps.

Memory and CPU activity look okay right now, but I see several apps that got very busy earlier today.

Storage, not so much.

Too little free space. That 56 GB is ~full. Free up a couple of hundred gigabytes, and see if the performance improves. Running a Mac with storage full reduces performance, and can cause instabilities and crashes.

What seems the Time Machine backup storage looks ~full, and there seems CCC and another backup tool or two around, too. Time Machine isn't fond of full storage, either.

I'd also run some performance tests without all of the external storage connected, as external storage can sometimes drag down aggregate performance.

Boot through Safe Mode, as that can clean up transient storage and can rebuild caches. (That probably won't get you a whole lot of storage back, but it's worth a try.

Remove the anti-malware and Cocktail, and test again.

The Google apps tend to be resource-intensive and doing who-knows-what, and I'd look to unload those to free up space and cycles.

This Mac has a whole lot of apps installed from a decade or more ago too, and un-updated. Microsoft Silverlight is long gone, for instance. More than a few other packages that either need to be gone, or need updates, too. Déjà Vu, etc.

Lots of disk-related tools installed. Presumably that was from prior to the SSD replacement that occurred here.

Launch Services appears unhappy, though that may be due to a lack of space, or some other issue.

I suspect the battery cycle count might be a spurious problem; that Mac should be good for ~1000 cycles.

Looking at all that's installed here, I'd be tempted to get a couple of backups, build a bootable installer, wipe this Mac and reload macOS 11.5.1, and then migrate in my files and documents, and re-install just the apps that are currently needed.

Please download and run EtreCheck, and then share the report to the clipboard. Then open a new reply here and then press the button that looks like a printed page to get a text input box big enough to paste the hardware and software configuration report here, and paste the report. From that data, we might see indications of the cause of the performance issues.