Anarchism

What you're describing is neither platformism nor synthesis.

Platformism and synthesis are both formalized ideas that some third party(ies) will be empowered to oversee and direct an anarchistic system, with the only difference being that platformism starts by decreeing the norms that will be required, while synthesis ar least vaguely nods toward anarchism by ceding the fact that no norms will ever be universally voluntarily held, but still then goes on to posit some body given oversight over the collective, and merely stipulates that they'll "allow" multiple viewpoints.

What you're describing is just individual interaction, which is in fact the only thing that anarchism can be based on. Yes - if the system is truly anarchistic, you'll be free to ally yourself with whoever you might prefer on whatever basis you might prefer, as, of necessity, will everyone else.

Platformism and synthesis are not ways in which you might choose to pursue that, but ways in which the entire process might be "organized." They're explicitly top-down ideas, which is exactly how and why they both fail.