I am developing an xlsform, the first question in section A is a multiple response with up to 10-15 options on official statistics. After the question, there are other questions in the section that link to the first question but I want if the respondent select 3 or 4 options the linked questions should only be asked about the those options selected.
You can use function count-selected(...) = 3 or count-selected(...) = 4 as relevant clause. See https://docs.getodk.org/form-operators-functions/#count-selected