They aren't special episodes but individual shorts listed in the movies part of our database.

Maybe this too... but this information is not from me, it's how Disney promotes it, even the posters are marked Special

They are released by Disney on separate movies pages :

• https://www.disneyplus.com/movies/the-wonderful-winter-of-mickey-mouse/2tcNDGM2b5HN
• https://www.disneyplus.com/movies/the-wonderful-spring-of-mickey-mouse/3mU9gmwEKpOI
• https://www.disneyplus.com/movies/the-wonderful-summer-of-mickey-mouse/3ErbaRhHXYL7

and not as part of the series https://www.disneyplus.com/series/the-wonderful-world-of-mickey-mouse/6PVlUlZEyNjS