At this point you’ll need to backup your stuff, setup a USB Bootable OS installer drive, wipe the drive down fully and reformat using the external drives Disk Utility (better than using the onboard recovery partition) to make sure you don’t have any Malware or Virus floating around. Reinstall the OS and before adding anything back install a good anti-Malware/Virus app/s to then check your backup drive. I would encourage you download fresh copies of your apps from the publishers as well.
How to create a bootable macOS Catalina installer drive
Also stick with macOS Catalina (10.15.x) don’t jump to Big Sur yet!
In its self this won’t fix everything, I would look at your RAM. I would talk with OWC to make sure the RAM they sent you is the correct SO-DIMM’s you might even want to get a fresh set. Unless you really need the full 128 GB how about taking 64GB out to see if that helps. Then swap the other 64GB in to see if one of the SO-DIMM’s is bad.
You appear to have a Samsung T5 external drive make sure you are using the thunderbolt port and don’t use it for your boot drive.
Heavy RAM usage - Apps are using a large amount of RAM.
Clean up - There are orphan files that could be removed.
Unsigned files - There are unsigned software files installed. Apple has said that unsigned software will not run by default in a future version of the operating system.System modifications - There are a large number of system modifications running in the background.
32-bit Apps - This computer has 32-bits apps will not work on current versions of the operating system.
Limited drive access - More information may be available with Full Drive Access.
Kernel extensions present - This computer has kernel extensions that may not work in the future.
Sharing enabled - This computer has sharing services enabled that could be a security risk.
Given the version of macOS you are running you should fully remove all of the 32-bit apps and extensions
3 32-bit apps
prl_hypervisor.kext (Parallels International GmbH, 16.1.1 49141 - SDK 10.11) prl_netbridge.kext (Parallels International GmbH, 16.1.1 49141 - SDK 10.9) prl_usb_connect.kext (Parallels International GmbH, 16.1.1 49141 - SDK 10.9) prl_vnic.kext (Parallels International GmbH, 16.1.1 49141 - SDK 10.9)
FTDIKext.kext (Wacom Technology Corp., 1.0 - SDK 10.11)
Dropbox.kext (Dropbox, Inc., 1.13.0 - SDK 10.14)
Wacom Tablet.kext (Wacom Technology Corp., Wacom Tablet 6.3.15-3 - SDK 10.11)