Only Export as plain text and Export in delimited text file can do it.
That’s not entirely correct. (Bulk) export to a database does append by definition, as well as export to Salesforce, Airtable, Power BI, and SharePoint lists.
The XML isn’t a tabular format, appending makes no sense.
Appending to file formats such as .dset or Excel can be done by importing a file entirely, using the “Append table” to append new rows, and then exporting back.