You can accomplish this - that is, generating multi-line labels - in KoboCollect, using a line break in a multi-line label; either manually entering it in the label string or inserting it via a calculated label. This form shows a few permutations:
Unfortunately, this only work in KoboCollect; Enketo has more limited support for markdown, and AFAIK there’s no way to readily accomplish the same; eg my same form in Enketo produces: