Is Duolingo accepted by IRCC?
If you are applying under the SDS program, you have to take IELTS academics or general (valid for the last 24 months) compulsorily.
Unfortunately, Duolingo is not an option for those applying for SDS. Luckily, the regular stream does not make it a mandate to take a language test. However, we highly recommend taking one of the English language tests such as IELTS academics, TOEFL etc.
Therefore, you could use Duolingo for your study permit application but IELTS academic is the priority as it may help in increasing your chances to receive an approval.