Yeah I had literally no idea what you were talking about until you mentioned the actual name in the comments.
NPM almost universally refers to node package manager in any developer or development adjacent conversation in my experience. Given that both the site, the command, the logo, and the binaries are “npm” makes that more appropriate.
Nginix proxy manager is far to niche to be referred to universally by acronym when it’s only ever used as an acronym when the context for it’s usage has already been defined (ie. In it’s documentation).
This becomes much more clear when you Google the acronym.