Based on the law, after living in the Netherlands for 5 years and passing the integration (inburgering) exam, immigrants can apply for being an official Netherland's citizen. Now the question is: If I take the exam in 2021, can I use the result three years later, or do they expire?
Once you pass all the integration tests (inburgeringsexamens) you will be eligible to get an integration diploma (inburgeringsdiploma). The diploma does not expire and can be used to apply for permanent residency as well as citizenship.
More information can be found on the official website of DUO.
I had the same question and called the ind. Apparently it wouldn’t be useful anymore because you will get a certificate saying that your dutch is A2 level. However after 31/12/2021 they require a diploma with Dutch level B1 , so it will not fulfill the requirement . I know that wasn’t the answer you were hoping for but this is at least was the answer of the ind when I called them.