Nintendo have announced that in early April 2024, online play and other functionality that uses online communication will end for Nintendo 3DS and Wii U software. This also includes online co-operative play, internet rankings, and data distribution.
Nintendo state that a specific end date and time will be announced at a later date, however also note that if an event occurs which would make it difficult to continue online services for Nintendo 3DS and Wii U they may have to discontinue services earlier than planned.
Nintendo do however state that it will still be possible to use Pokemon Bank but that online services for that may also end at some point in the future.
So really to sum up the writing is on the wall for 20+ years of backwards compatibility for Pokemon Games.
I'm sure many people have migrated their collections, however I certainly plan to migrate one of each Gen 3 event Pokemon we have managed to obtain over the years. Many past Pokemon Event Distributions are available in our Pokemon Content Download Forum for anyone wishing to distribute some of their own past events today in 2023.
Source: Announcement of Discontinuation of Online Services for Nintendo 3DS and Wii U software