Hi @William Watts
You could grant edit permission for the specific users in the document library. Then check their permission in site permission to see whether they have read permission, what's more, you need to check that in Site Page library or just home page they also must be granted only read permission.
As a result, we could only upload files but not add/edit web parts as you could see in the screenshot it is blank in the top right corner ( in common there is a button for edit) :
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