Biological sex isn't binary. There are various markers, most of which exist on a scale, and they correlate with each other and gender, weakly (height) or strongly (genitalia size). Sexual arousal by stimulation and over time is one of them.

These markers can change over time or with medical intervention generally known as gender-affirming therapy, which helps people who feel their gender and biological characteristics don't correlate enough.

Still, we use labels like "biologicaly male" as a shorthand for "the sex markers considered decisive by me or my culture correlate(d) with the male gender (at birth)" and for legacy reasons (some legal forms and people still ask about binary biological sex but I'm looking forward to this being abolished). Yes, as an ex-Christian I used to have the outdated view of gender too and it took me a while to learn all this (and arguably, I still have things to learn) but thankfully, I'm open to becoming a more accepting person and there are great free resources online.

Your meme is a bit reductive but no big deal, it's on par with the format and you've demonstrated openness to the nuance in the body text. Just trying to prevent people from correcting you rudely.

Edit: thinking about if "legacy" is a good descriptor of many people's understandong of gender, turns out pretty good − much like IPv6 is the modern standard but "legacy" IPv4 is still in wide use. When someone asks "What's your IP address?", you can supply them with IPv6, which provides extra nuance but is not as supported as IPv4, which on the other hand cannot cover the needs of more than 4 billion people. Some people refuse to learn hexadecimal and will refuse to connect while others are stuck in legacy systems that will not allow them to implement IPv6 (although they may have some levels of compassion, and will be ready to communicate via tunnelling protocols). While IPv6 covers everything one expects from IPv4 and much more and is arguably inevitable, the legacy is so deeply rooted in how we talk that it's really hard to replace and some ISPs try to indefinitely postpone the update. If you choose to bottle up and say your IPv4 address though, you might be missing out on genuine connection options if the other side also supports IPv6. (This analogy works better with languages which don't differentiate between "sex" and "gender" in one word and asking for pronouns instead is uncommon and/or impractical, like Czech.)

(My Czech pronouns are on-ten/něho-toho/němu-tomu/něj-toho/×-ty/něm-tom/ním-tím btw and nobody has ever asked for them.)