Hi Ben
The short answer is - no - there is no appearance setting that will give you the first/last name of the logged in user.
My first thought was that you could maybe use an API call to figure out the username/first name/last name:
https://developers.arcgis.com/rest/users-groups-and-items/user.htm
But it seems you need to be an admin to get that information returned because of privacy concerns.
So your best bet would be a hosted CSV file linked to your survey - but like you say you will have to manually update that CSV file, even though it will be automatically linked to your survey.
https://doc.arcgis.com/en/survey123/desktop/create-surveys/xlsformformulas.htm
Look at "Working with external content":
If you manually place the .csv file in the survey's media folder, and at a later time upload a .csv file of the same name to ArcGIS and link it to the survey, the .csv file in the survey is updated from the linked content (if newer).