Hi, yes you can upload documents from digilocker for your NIOS class 12th. There are few things that you should keep in mind, if you are applying for NIOS class 12th immediately after finishing class 10th then you won't be eligible to sit for all the subjects in one attempt.

Below is the link for you to take a look at for the criteria and the procedure. Also, if possible always keep a soft copy of all your documents on any device so it is easy to assess while filling out your form. Hope this helps.

https://school.careers360.com/articles/nios-admission#NIOS-2021-Admission-Eligibility-Criteria