You made a few mistakes here:
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You placed media in the Plex shared folder contrary to the warning to not place media there.
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You compounded the error by selected “Libary” to scan instead of “Libary/target folder”.
This resulted in PMS scanning itself and creating an infinite loop which causes it to fail.
This is well known to happen and why I place those warnings about not putting media in the Plex share.
So, Contrary to what you’ve seen on the internet, may I suggest you reorganize your media and then proceed to setup Plex the proper way?
Please read this guide which will also serve as a recommended setup method.