As a Roblox developer, it is difficult to retrieve an up to date list of a players online friends in a server script. We are currently using GetFriendsAsync and GetPlayerPlaceInstanceAsync together with MessagingService for fast real-time updates.
Using GetFriendsAsync it is possible to retrieve all friends just fine, but this hits request limits pretty hard unless you only use it once every 3-5 minutes or so per player, especially when it needs to be used in conjunction with GetPlayerPlaceInstanceAsync to fetch the PlaceId and JobId of the friends who are online. This is not fast enough for any sort of real-time friends based gameplay or quickly joining online friends from an in-game menu.
GetFriendsOnline doesn’t seem to have the same issues as the above method does, and also provides both a PlaceId and JobId for the friend data, but for some reason is limited from being used on the server. If GetFriendsOnline were to be unlocked for use on the server, it would solve the rate limit issues mentioned above for our use case.