This questions is always an interesting one because im actually very good friends with a few of my exs. Then there’s the few that i have no communication with at all i still talk to their friends just not them.
I feel that no one will know you better then you ex and then but not even entertaining the idea of being friends you could miss out on a great friendship after all friends could be the most you were meant to be. Its only gonna work if you establish boundaries. Since the dynamic of you relationship is gonna change if you dont deal with that it will lead to alot of awkward situations further down the line. Any unresolved issues from the relationship need to be resolved and both parties need to be able to step back and be happy as a friend for the other.
On the other hand having an ex as a friend could just be a big mistake im all for it but i dont think it is for everyone. It could lead to you repeating the cycle of getting back wit your ex if either of you have feeling or can end with one of you being hurt unnecessarily.
Its one of those questions with no definite answer just opinions, it varies from person to person and situation to situation