Four years after its initial release, it has been confirmed that Mario Kart Tour will no longer receive new content following the "Anniversary Tour" update on September 20.

The details:

Following the Anniversary Tour, Nintendo and DeNA have announced that all future updates will reuse content from previous tours released over the past four years. “No new courses, drivers, karts, or gliders will be added following the Battle Tour starting 04/10/2023,” the in-game message reads. “We hope you continue to enjoy playing Mario Kart Tour.”
The decision appears to be part of Nintendo's plans to move away from Mario mobile titles after a decade of mixed success. Shigeru Miyamoto, the series' creator, stated earlier this year that "mobile apps will not be the primary path of future Mario games" after the company struggled to translate traditional Mario gameplay to mobile using a touch screen. However, Nintendo has mobile titles in the Animal Crossing, Pikmin, and Fire Emblem series that appear to be here to stay for the foreseeable future.
The sixth and final DLC for the Nintendo Switch's Mario Kart 8 Deluxe will include tracks created for both titles, which will be released by the end of this year. With the end of Mario Kart Tour content drops, both entries will now receive their final updates around the same time, implying that Nintendo's rumored Switch successor could launch with a brand new Mario Kart title.

More Nintendo news:

A well-known leaker claims that Nintendo will make an announcement about the F-Zero franchise during a Nintendo Direct later this month, possibly marking the series' first new release in nearly two decades.
Nintendo reportedly showed its new console to developers behind closed doors at Gamescom 2023, with the system powerful enough to run Epic's The Matrix Awakens demo, which was previously used to demonstrate the power of the PS5 and Xbox Series X/S.

Mario Kart Tour will no longer receive content updates