I've been over this dilemma multiple times.

For me, what would matter is the status of the name, and not the domain. You say it's quite popular and most extensions are taken - why use it then? It will diminish your chances for standing out and having a memorable brand.

If your name is unique, is a good fit, specific for your space, not trademarked etc., then great! But in that case you are fine with any extension. getting "getbrandname.com" instead of "brandname.app" won't make or break your project.

If your name doest not fit the above criteria, pick a different one. Go wild, go bold. I suggest the book 'hello my name is awesome' (bad title, but on-point, actionable content) if you go ahead.