all ?p=hdwvshhe means is someone is trying to access some WordPress content with the ID of hdwvshhe. This would suggest that content doesn't exist anymore/never existed. the ?p= is just the parameter to say 'Content ID' essentially. Depending on the frequency of that error it could be malicious or it could just be accidental bookmarking of old content etc

The default Plain Permalink also called the Ugly Permalink looks like this: http://example.com/?p=N with p as the parameter and N is the unique ID of the post or page in the database. WordPress comes preinstalled with this setting. It works on all server environments. It is not user-friendly and also not optimized for search engines. You can learn more about Permalinks structure here: https://wordpress.org/documentation/article/customize-permalinks/#:~:text=Permalinks%20are%20the%20permanent%20URLs,changed%20%E2%80%94%20hence%20the%20name%20permalink.