You should be able to use two expressions to do this when collecting new features. There is a demo I did for the Dev Summit available on YouTube here which shows this scenario. Here is the TLDR version with some sample data:
Say you have 3 fields for collecting information about a tree:
1. "has_fruit" which is a coded value domain with "Yes" and "No" options
2. "type_of_fruit" which is coded value domain with "Apple", "Orange", "Other"
3. "other_fruit_name" which is text
You can define an expression for "type_of_fruit" so it only shows if the tree has fruit like:
DomainName($feature, "has_fruit") == "Yes"
You can then define an expression for "other_fruit_name" so that it only shows if "type_of_fruit" is other like:
DomainName($feature, "type_of_fruit") == "Other"
Since "type_of_fruit" will only appear if "has_fruit" is "Yes", then "other_fruit_name" cannot be filled in, which means "other_fruit_name" won't appear (unless there is a default value applied for "Other").
In the case of updating an existing feature, it's possible that there are existing values which could cause the "other_fruit_name" field to appear. This can be solved by extending the second expression to also check that "has_fruit" is "Yes":
DomainName($feature, "has_fruit") == "Yes" && DomainName($feature, "type_of_fruit") == "Other"
