Things appear to have changed in that tests taken only now are accepted until Juli 1, 2025. And if the test system passes the Q-Mark by then (which I take to stand for quality requirements), it will keep being accepted beyond that date.
The SDS test centers list dates next year, they appear to accept applications.
See the List of Accepted Certificates, and footnote #6 on page 3.
The SDS certificate is still recognized as a Swiss test for immigration and citizenship procedures until 30 June 2025. If the test reaches the Q-Mark before this date, this will be communicated here. If it is certified by the Q-Mark, it will remain on the list beyond the date of July 1, 2025.
https://www.sem.admin.ch/dam/sem/de/data/integration/themen/sprache/anerkannte-sprachzertifikate.pdf.download.pdf/anerkannte-sprachzertifikate-d.pdf