So from the latest MakingStarWars podcast:

Jason heard about Obi-Wan’s show about three months ago, but then he got a signal that it wasn’t greenlit at that time so he didn’t make an article. He doesn’t know if it’s greenlit now.
He heard it’s 6 episodes as previously said in SWNN’s report.
Jason also seconds that Ewan McGregor was on Solo’s premiere because they indeed wanted to announce Obi-movie after some time.
The series’ script is based on the events from the movie’s script.

Also the show has begun pre-production:

https://www.fanthatracks.com/news/film-music-tv/star-wars-tv-production-begins-in-the-u-k/

“Tonight we can reveal that the third as yet unannounced Star Wars TV series will be shot in the UK under the production name of SERIES III PRODUCTIONS (UK) LIMITED which was registered on the public UK companies register on the 12th October 2018. We anticipate that the focal point of the series will be revealed at Star Wars Celebration in April. It should be noted that for convenience Disney register businesses in blocks, and the creation of these businesses does not mean they started production at those dates, merely that they intend to enter production soon. This can of course mean very early design development, and does not necessarily mean they will see final production, as seen recently with PLT Productions (the Kenobi movie.)”