Heterosexual, attractive men and women can be friends by default. Not on purpose.
Let me give you a few examples of default:
-I have a male friends who works in my office we are friends because we work together
-I have a male friend who is married to a woman I am friends with
-I have a male friend who is dating one of my female friends
-I have a male friend who is on my young adult core team at church
In all of these scenarios, I have a friendship with these men (we share inside jokes, laugh together, enjoy each other’s company). However, the friendship exists through something or someone else.
If any of these men were going out of their way to be friends with me on purpose (i.e. hanging out one-on-one, staying up late talking together, going on a trip together just the two of us-things that I could do with my female friends and no one suspect anything more than a friendship), there would be more than a friendship whether one of us was saying it or not.
In adulthood (in the US usually means after college) you can’t have just friends of the opposite sex on purpose-only by default (any of the examples I listed above).
I’ve never experienced a male going out of his way to be friends with me without wanting something more.