The most common fixes are re-associating the file to PSP.... or to uninstall, then reinstall PSP. See the links below:
https://answers.microsoft.com/en-us/windows/forum/windows8_1-performance/paint-shop-pro-images-pspimage-display-as-icons/8885c9f3-55d4-4400-bf87-022017646671
https://forum.corel.com/EN/viewtopic.php?f=56&t=63186&p=353420&sid=f407f213faa49b5b63256f96877058a5
If neither of those options work, there is a PSP Thumbnail handler that has worked for many. See the link below::
https://www.botproductions.com/pspthumb/faq.html
Hope this helps.
Grif
I am using a Laptop with windows 10
I am using "Paint Shop Pro". When I save an image I can't see PSP thumbnails on my Laptop? All I can see is this;
I have the Folder option to show thumbnail but it still will not show them

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