Is there a way to do a perch_blog_custom to display blog posts only by a certain author?
You can get all the posts by Author...
Here are all the Blog Functions: https://docs.grabaperch.com/functions/blog/
Yes, you can use the author option which takes the value of author slug:
'author' => 'john-silver',
You'd often get the author slug from the URL. For example, if your URL is /blog?author=john-silver:
'author' => perch_get('author'),
Thanks Hussein! That worked.