Author page = Error 404

When I click on an author name/link it gives me the <my URL>/?author=<author#> page with “Ooops– Error 404”. i found a forum item from someone else with the same error (https://forum.tagdiv.com/topic/author-page-not-working-getting-404/). I tried resaving the permalinks (I am using Plain) and clearing the cache, but it didn’t help.
Even when I go to Users and click View for any of the users, I get the same 404 error.
I tried adding a new user, and then clicked View for that new user = same 404 error.
It looks like every time it generates a page <my URL>/?author=<author#>, it generates the 404 error.

Thank you, Simion, for your quick and helpful response! You guys are great!
I discovered that the WordFence plugin was blocking my /?author= link for security reasons. I was able to disable this one protection and still use WordFence, so it solves my problem. Thanks!
Two follow on questions:
* I didn’t have to try changing themes, but would I have a problem changing to another theme to test something and then change back to Newspaper? Would all of my Newspaper theme settings be saved?
* It seems that websiteURL/author/authorname does not work on my WordPress, just websiteURL/?author=ID. Should my site using the Newspaper theme allow both link options?