you are probably talking about making a mod.
if so, i can assure you that EVERYTHING is possible in minecraft modding. things like new blocks, biomes, weapons, mobs and similar things are only scratching the surface. i personally dont know how to make mods, but i have played a lot with modpacks which include hundreds of mods, each changing the game minutely, and together granting an experience nearly completely different from the vanilla gameplay. this may not help you in your attempts to create custom content for minecraft, but at least now you know that these are called mods, and can research the creation process from there.
you can download other people's mods on sites like curseForge, or try out premade modpacks on the Twitch launcher.
next, i want to tell you that i am sincerely sorry that the minecraft community has let you down in answering your questions. biggest apologies.
lastly: trans rights, sister. keep fighting.