Box 1: No -
User.name is a property.
Box 2: Yes -
Box 3: Yes -
The coalesce() function evaluates a list of expressions and returns the first non-null (or non-empty for string) expression.
Reference:
https://docs.microsoft.com/en-us/composer/concept-language-generation
https://docs.microsoft.com/en-us/azure/data-explorer/kusto/query/coalescefunction