Hi Frank,
This is currently not possible in the ACF addon.
The idea was that the return / display format of the ACF field should be returned but this is currently not working. I think that the return value should be used instead of the display value becauses ACF says that the display format is for editing. What do you think? I’ve created a ticket for this https://github.com/codepress/admin-columns-issues/issues/363
You can show only the year by adding a custom field with Field Type set to date. Then you can set the date format to ‘Y’ to show only the year in the column. Please be sure that you don’t use inline edit for this column unless you know what format is used in the database. ACF stores its date data as format ‘Ymd’ so you’ll have to use this format when you use inline edit, not only set the year. It’s a workaround but it should give you only the year as a column.