Doujinshi can be added to the website if it meets all the following criteria:
The doujinshi is by an already serialized mangaka.
It meets the Japanese 'Country Of Origin'.
The doujinshi is not based on existing published material (anime, manga, manhwa etc.) - it must be an original work.
Doujinshi is not a format on AniList, instead, you have to the toggle the Self Published option.