It's "Beyond me".
For example: It's beyond me understanding why you made that mistake.
Beyond me is usually used when we don't know the reason behind something.
But that will also depend on how you'd use "Além de mim" in Portuguese.
Here 2 more options for you:
Além de mim, havia outros profissionais no evento.
Besides myself, there were other professionals in the event.
Ninguém fará essa tarefa além de mim.
Nobody will do this task but me.