grammatical number - Which pronoun should I use when writing about a generic activity in a thesis?

I'm writing my Bachelor's thesis where I describe students' activities in a dormitory.

A student produces with a valid ID or passport here and hands in an ID
card photo. In case he/she has a reserved room, there is prepared a
printed dormitory agreement.

Should I use only plural in the whole document or is singular form also applicable?

Answer

The singular, as you have used with A student produces... is not only possible but may be clearer than the plural. This is because with Students produce...ID photos, it would not be clear whether each student should produce one photograph or a set; A student produces a photo is unambiguous.

Whichever you choose, do check (repeatedly) that you remain consistent throughout the document. If you start Students produce their valid IDs and later go on to a dormitory agreement, it would be reasonable to assume that only one agreement is produced per dormitory. Conversely, A student arrives with a valid ID which later mutates to their passports is arguably ungrammatical, and quite possibly confusing.

(Note to supporters of singular their; the word was 'arguably'. Your dictionary citations do not alter the fact that it is controversial , and therefore best avoided in a thesis written in your second language. Can we please not have this same argument every time the point is mentioned?)