Import an xlsx file to Oracle SQL Developer and interpret it as a table I have an xlsx file with content in the form of a database table - first row is column names, and columns contain varchars2, integers etc.

Since VBA and Excel worksheet functions are too slow for it, I want to view and manipulate it in Oracle SQL Developer, Version 19.2.0.206 developer. Everything occurs locally, there is no existing database connection, and none available.

I attempt to do this by clicking "new connection" (below screenshot; in German), but it prompts me to enter information for a database connection that I cannot have, because there is none yet. 

When I try to make up a username, password, and use the below seen default hostname, port etc., and click on test, it shows: I/O error: The network adapter could not establish the connection.

Is it possible, and how do I achieve, that there is a "dummy" "connection" that is not actually connected to anything existing, but allows me to turn a suitable xlsx file into a table for data manipulation?

I have access to MS Access, but I hate the interface and have more experience with Oracle SQL, so I would appreciate a solution with Oracle SQL
No.  SQL Developer is just a client that interacts with an Oracle database.  It is not a database in and of itself so it has no way to store and manipulate data other than via an Oracle database.

You could download and install an Oracle database on your machine, connect SQL Developer to that, and use the SQL Developer wizard to load the Excel file into a table you create in this new Oracle database. But that is a decent amount of effort to go through just to deal with a single spreadsheet.