I guess that depends on what you mean by "absolute" solution. All known workarounds are in the "How to Stop Ad Popups" sticky -
https://forum.corel.com/viewtopic.php?t=65942 which points to several support articles by Corel on how to accomplish this, both the official and extreme options.
For me, deleting the Messages folder always solves the problem if pop-ups occur after I've turned off the Messages options. This is usually because old messages are still downloaded. So deleting them starts me fresh.
1) Close PSP if open
2) In File Explorer type %appdata% in the address bar
3) Go to the Corel Folder
4) Delete the Messages folder
5) Open PSP and make sure the messages options are still disabled. The messages folder will be re-created but it should have a Messages.policy file that says "opt-out" in all communications.
If that doesn't work then I point you to the official recommendation by Corel.
Their most recent 2020 article -
https://kb.corel.com/en/127276
Suggests that if the normal method doesn't work, then disable the tasks.
If the recommended solution does not work for you, I suggest to disable or delete the CorelUpdateHelper
1. Using the search box, to the right of the START icon from Windows, type: Task Scheduler and press Enter
2. Click on Task scheduler Library
3. Locate CorelUpdateHelperTask, right-click and select Disable or Delete
4. Locate CorelUpdateHelper TaskCore, right-click and select Disable or Delete
5. Click the X at the top right to close the dialog box
