This members-only tutorial shows a couple of ways for retrieving user meta - built-in as well as custom fields created using ACF (Advanced Custom Fields) in WordPress for the author of the current post.
These functions can be used either on singular views or on an archive in the loop.
Note: Use only one function. Either should work fine for retrieving built-in user meta and ACF custom fields. It makes sense to use the ACF version when custom user fields are set up with ACF.