High CPU on an iMac 2019 with 128GB Ram???

This certainly throws up a red flag:

Top Processes Snapshot by Network Use:

Process Input / Output (Source - Location)

Other processes 151.69 GB / 11.21 GB (?) ⬅️

com.apple.WebKit.Networking.xpc 5 MB / 352 KB (Apple)

parsecd 70 KB / 3 KB (Apple)

Safari 14 KB / 2 KB (Apple)

homed 4 KB / 829 B (Apple)

Something is homing home with a vengeance. Could be your VPN which is probably not doing much anyway, or OneDrive.

I suspect the VPN over OneDrive. Removal depends on the app develper.. Check with the VPN developers for instructions of disabling or, better yet, removing it.

https://openvpn.net

There may be an uninstaller in the OpenVPN folder.

If you can't find the developer's instructions to uninstall OpenVPN try the following;

1 - boot into Safe Mode by booting with the Shift key held down

NOTE: Safe Mode boot can take up to 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE:  if you have a wireless keyboard with rechargeable batteries you may have to connect it with its charging cable to assure a boot into Safe Mode. 

2 - download and run the shareware app Find Any File to search for any files with the application's or the developer's name in the file name.  Do the following search: 

1 - Name contains openvpn

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.  

RAM has little effect on speed. The culprit is likely the relatively slow read/write speeds of you 7200 RPM hard disk?