immaterial / trivial

It depends on context – their meanings are not the same. When assessing ROMM you would generally talk about material/immaterial.
“Clearly trivial” is mentioned in some ISAs – most notably ISA 450 (“the auditor shall accumulate misstatements identified during the audit, other than those that are clearly trivial”). ISA 450 goes on to say that clearly trivial does not mean “not material” – but will be of a wholly different (smaller) order of magnitude. So, for example, if 5% of profit is $100,000, a misstatement of $40,000 is not material, but I doubt it would be considered “trivial” (whereas $4,000 might be judged trivial).
Trivial is also used in the Code of Ethics. For example, in relation to gifts and hospitality, value is assessed in the context does it pose a threat? (Which has nothing to do with the concept of materiality in financial reporting.)

I am still not clear on what it is you are asking. If when you are planning an answer to a part of Q1 which is asking about ROMM you have lots of ideas some of which are material and others immaterial, your answer should be based on what is material. You might however say that something is immaterial/not material in money terms, but is material by nature (e.g. see RPT in D18 answer).

In a completion/review Q, however, where there are matters outstanding/uncorrected misstatements to be evaluated, although you would expect most of the matters to be material (otherwise there would not be much to write about), there could be matters to be assessed as immaterial (e.g. item iii in Q2 S18).