so pan is where you like all genders, and you don't have a preference, it can also be called genderblindness
bi is where you only like 2 genders (it can be different than just boys and girls, for example you can like only girls and nonbinary ppl) and sometimes you have a preference, and usually you can still like MTF ppl or FTM ppl :3
also as someone who used to think I was pan, pansexual ppl are literally so tired of the 'liking pans' joke it isn't even funny anymore, you arent original, please stop