The issue is definitely caused by other versions of the DLL being already loaded in memory. Disabling all other programs from running at system start isn’t guaranteed to fix the issue either; on Windows 10 and 11 (not sure about earlier versions) some programs will run some DLLs or services immediately in the background even when the program is not allowed to run at system start.
In order to manually fix the issue, you need to use file explorer to search your entire system for “qt5” to see where each instance of the DLLs are located. (This can take a long time on HDDs. Don’t close the window, be patient.) If file explorer doesn’t let you see the full file location, then left click once on the file and hover your mouse over the partial file location. A popup will show over it showing the full address. Do not close the window you did the search in or you will have to so the search again.
Open a second file explorer window and navigate to the file location of one of the DLLs in your search. Open a third file explorer window and navigate to your GPlates install location. Copy all DLLs in your Gplates folder that start with qt5 (there should be 8 of them). Paste them all into the second file explorer window. When prompted, select “Replace the files in the destination”. Then, select the check box for “Do this for all current items” and click continue. If you are not able to complete this step, you probably don’t have administrator privileges. Sign in to your admin account or contact whoever is in charge of your computer system.
If the copy completes without any errors, then that instance of the DLLs was not the problem. Repeat the above steps for the next instance in your search results. Eventually, you should get an error saying that the copy can not be completed because the DLL is open in a program. This is your culprit (or at least one of them). Open task manager and look for any services or programs in the background processes section that are from the program in question. Rick click the service and click “End task.” Then try the copy again. If the copy works, then your problem is hopefully solved. Restart the computer and check. If the problem persists after the restart, then there is another program running the DLLs at system start. Sorry. Do the process all over again until you find the next program that is running in the background.
In my case, there were two programs that were causing the issue; Private Internet Access and ReallusionHub. Disabling the programs from running at system start did not work because the programs don’t care what you tell them to do, they run anyways.