Does a Bernoulli trial have to have a .5 probability?

No. A Bernoulli trial just has to have only two possible outcomes. Heads or Tails? Boy or Girl? etc. Although these examples might appear to have a pr of .5, it doesn’t have to. For example, if you have a classroom full of 20 people and you randomly pick a person in the room, they are either male of female But suppose there are 15 males in the room, the probability of picking a male is .75, not .5