Thanks so much for your reply BDAqua --
My other Library Folder is OK. I'm familiar with the other folder and have accessed it for various reasons. I've had Mac computers since 1986, and in the past the Library Folder wasn't hidden. But, I completely understand why it is hidden now.
Anyway, I did a lot more investigation after I posted my question, and here's what I found:
The folder isn't dangerous and I'm not the only person who discovered an odd library folder in Documents. I have no idea why it took me such a long time to notice its existence.
The folder appears to be related to Adobe CC, which is installed on my MacBook Pro.
My Adobe Creative Cloud Installer version: 5.5.0.617
Now, I have to delete it, following Adobe's instructions.
I hope the info I'm providing here is helpful.
Here are links related to the same folder issue (Apple Discussions , Adobe, etc.):
https://discussions.apple.com/thread/252516978
https://discussions.apple.com/thread/252514537
https://discussions.apple.com/thread/252513107
https://community.adobe.com/t5/download-install-discussions/library-folder/m-p/11868658
https://helpx.adobe.com/download-install/kb/library-folder-created-on-macos.html
https://community.adobe.com/t5/creative-cloud-services-discussions/last-creative-cloud-update-create-a-new-library-folder-on-macos-big-sur/m-p/11915817#M22479
https://apple.stackexchange.com/questions/414851/a-library-folder-appeared-in-my-documents-folder-on-mac-is-that-normal
Here's a screenshot of the Get Info panel (which shows that the little gear did not provide any drop down options...). I opened the lock, and then closed it...
