In an interview with IGN, Shigeru Miyamoto, the creator of Mario revealed that Nintendo is always working on the next Mario game. They are just waiting to share more information on the next major game release. Nintendo recently opened a Mario-based theme park in Hollywood and will be releasing a movie of the same franchise. So it makes sense for them to wait before revealing the next game.
Super Nintendo World is the name of the theme park that opened up in Hollywood. It includes many of the popular Nintendo characters including Super Mario. If you have some free time, and are with a family and kids, then this theme park should be on your bucket list of places to go on your next vacation. Nintendo is also producing a Mario-based animated movie so they have had a lot on their plates. Which is the reason Nintendo does not have any new information to share about the next Mario game at this moment.
As mentioned, Miyamoto said they are always working on Mario, and would certainly share information when the time is right. The last major Mario game that was released was Super Mario 3D World + Bowser's Fury back in 2021. Before that was the release of Super Mario 3D All-Stars in 2020. So it seems like Nintendo's next Mario video game release should be just around the corner.