FR campaign setting has a section on druids and how they fit into the world, which gods allow for druids etc. I don't have the page number because I don't have the book in front of me right now but it's in the low to mid 20's IIRC.
Beyond that, I believe the book also describes some druidic circles in FR and how a spesific grove works. However, like most things in and that are related to specifics in groups or organizations, its been left very open-ended since most dnd games that involve druids involve PC adventuring druids or custom made groves controlled by a games DM. The FR book on deities also have some druid spesific stuff in them that is unique to whatever deity they worship, such as a spesific ritual or holiday that is observed or aspect of the class that is given special attention.
I know of one third party book that offers some potential hooks or ideas,
the quintessential druid however IIRC its not FR spesific but base dnd, and it's not canon as its third party so take it all as a general guideline or place for ideas rather than actual lore. However it can give some ideas on how to play a druid or plan a druidic circle, but its important to keep the spesifics of FR druids in mind as it sets them far apart from base druids in some aspects, mainly the requirement of specific deity worship rather than a more ambiguous worship of nature as a whole a long with some other differences.
Also this topic would probably be better if it was in the lore subforum not the improving amia one so I'll move it since its a question about amia or fr specific lore.