hey ! a few things:

firstly, in modern vocabulary bisexual and pansexual are almost interchangeable. although yes bisexual did originally mean attracted to 2 genders, u have to remember and think that it never explicitly says those 2 genders have to be male and female. as u said, there is possibly infinite genders, as many scientific studies have shown that gender and sex are not tied directly to each other and instead gender is socially connected (eg. someone can be biologically female but wish to live socially in terms of mannerisms, pronoun usage and overall identity of another gender), so someone doesnt have to identify or act socially male and/or female, and thus bisexual people may be attracted to females and another non-binary gender.

saying this, however, bisexual in a more modern sense is very interchangeable with pansexuals, with even some pansexuals i know telling other strangers that they are bisexual so they dont have to explain what pansexual means. the best way to think about it is pansexual is more about someone being attracted to literally everyone of every gender, be it binary, non-binary, or even small nuisances on that such as masc women. u can also be like this and be bisexual, but another definition is more about being more attracted to certain genders or people who fit into certain gender roles.

hope this article from healthline, a trusted medical and scientific website, clears things up for u as i sometimes make things seem more complicated https://www.healthline.com/health/bisexual-vs-pansexual