If you are interested in NPD you could really read up on the topic. If you want to know if you have npd symptoms I would suggest to ask people who you trust and who know you well. Ask them, then listen carefully, and if 3 independent people tell you what they think of you, believe them.
Do not ask them suggestive questions, but try to ask fields or topics that npd people can have symptoms or indicators in.
Voyager because its a name of a thing and install because the Webapp is not really installed, it’s just a bookmark in safari that’s opened without the toolbars etc
As others have written it’s deconstructive towards other people plus NPD are hard to make understand their behaviour is problematic. In their view you are the problem if you have a problem with them. Depression, ADHD and other things do not have that trait. With them you can talk them into therapy and about potential problems they are causing.