That’s simply incorrect. Most of the innovations in Modern Hebrew (relative to Biblical Hebrew) came in the Mishnaic period, early CE. Hebrew continued to be used as a liturgical language, and occasionally a business language, both in its Biblical and Mishnaic forms, until the 1880s (not 1920s), when the Zionist movement brought it back into use for casual speech. The Hebrew used in the Mishnah is quite close to the modern written language, though it lacks modern words and some very recent innovations like topic-first sentences.