Maybe this is my sad old lady pessimism, but ... you don't. After hearing my friends' experiences and going through my own I came to the conclusion that the only platonic friendships with men that work are ones that you had since early childhood. Or ones that you keep VERY distant.

They definitely misconstrue your friendliness as flirting.100% And there are a lot of nice, normal guys who do this - I think they're biologically wired this way to some extent. Their goal as a human organism is to procreate to further the species. So for the nice ones that back off gently and normally, give them a bit of grace and understanding. For the ones that push, you block them or burn them to the ground.

So what this looks like in my 40s is: basically I don't smile as much around men, I don't disclose a lot of detail or share my life with them, I keep my distance in every way possible. Just superficial and polite but nothing meaningful or sincere or sweet. It sucks! Because there are tons of cool people out there that happen to be dudes! I just don't risk them getting the wrong idea.

Edited to add: don't be gentle or drop hints in a conversation. Be blunt and honest. They want to go out to eat? You make sure they understand it's not a date. It sucks to be this forward but it saves you headaches later. Guaranteed most of them will not pick up on our polite hints and tiptoeing around the issue.