On November 16, 2021, Google announced an updated timeline for their retirement of classic Google Sites that extends the previous dates to summer 2022. Your ability to edit classic Google Sites now ends on June 1, 2022 (previously December 1, 2021), and Google will begin deactivating those sites on July 1, 2022 (previously January 1, 2022).
Nevertheless, you should still convert your classic Google Sites to new Google Sites as soon as possible. The longer you wait to make the transition, the greater the possibility for data loss when Google begins the deactivations. If you currently own a classic Google Site, refer to Convert Your Classic Google Sites to New Sites for more information on how to convert your classic Sites to new Sites.