Thanks for that! The video helped me realize that the problem was not that I couldn’t create the database, but that I already had, and just didn’t realize what the terminology was referring to :/ So, by unchecking the “Create database” option, everything worked fine!
Except, when I went to do the post-install steps, I couldn’t get into wp-admin. For whatever reason, that entire directory was missing from my server. Is there something I did wrong? I manually uploaded wp-admin from the clean install of WordPress, so that problem is solved, but I’m anticipating further problems if I accidentally made some mistake along the way.