Hi.
It looks like this could have to do with the way data is imported and interpreted in ArcGIS Online. ArcGIS Desktop is reading the geodatabase domains and presenting to you the code descriptions that Survey123 created. ArcGIS Online, on the other hand, is reading the values, rather than the descriptions.
The Survey123 Web Designer hides much of the complexities of building choice lists: We only ask you for the description of your values in the list. For the values, to avoid issues with non-ASCII characters we create corresponding values of choice_0, choice_1 etc So essentially, the descriptions read the way you want it, and the actual values in the database are more cryptic. Very often nobody cares because the clients display the descriptions but in your particular workflow somewhere in the process the descriptions are lost and Online ends up showing the internal values.
I think that if you simply take your File Geodatabase and publish it as a Feature Service, you will end up having properly created domains in ArcGIS Online (and you will see the descriptions rather than the values). I am afraid adding your File Geodabase to My Content directly is somehow losing the domains.
If these internal values annoy you, you can alternatively download your survey into Survey123 Connect and edit the values in your choice list manually. In this manner, even if you look at the values directly, rather than the description, they will make sense to you.