I think Jcomm is on the right track. Default seems to work only when defining a profile for a specific aircraft. Apply to All Aircraft, I think as Jcomm implies, is for generic application of a profile across that class of aircraft (or wider).
I've watched several useful YouTube pilots, including J Beckett and SimHangar, on Custom Views, but a 2024 manual seems to be an important tool for us these days.
Keep your chin(s) up guys. I'm still plodding on. I trust the community.
Barry