Is there a reason you are not using the latest version of Collect - v2023.2.4?
Styling should work on choices - although just in Collect, not in Enketo.
+-----------+------+---------------------------------------------+
| list name | name | label |
+-----------+------+---------------------------------------------+
| options | a | is this _italic_ text? |
| options | b | is this **bold** text? |
| options | c | is this <span style="color:red">red</span>? |
+-----------+------+---------------------------------------------+
You're correct that there are differences between how Enketo and Collect handle the styling and not everything works on both. When the new web forms are released, it should solve these issues: