According to a rough translation, this means it's no longer accepting repairs for this particular unit as of 28th August 2024. Repairs for the New 3DS have also been discontinued in other locations around the world. On the plus side, repairs for the 2DS and 3DS XL in Japan are still available until Nintendo's stock runs dry.
Nintendo: "As we have run out of parts necessary for repairs, we have stopped accepting repairs for the New Nintendo 3DS system [KTR-001] as of August 28, 2024."
This announcement follows the shutdown of the online play for the 3DS earlier this year in April. In July, Nintendo also announced it had run out of replacement parts for the Wii U in Japan and would be ending the repair service for this system.