Most geopolitical rivals already blocked US social media - Russia, Iran, China. Brazil blocked and forced X to censor opposition Brazilian politicians. It's already happening.

EU/NATO members can't outright block US social media for obvious reasons (military protection is not free). They try to do sneaky things to control social media with DSA, etc.

India/Indonesia and a few other countries are already debating banning foreign social media companies. India was the first to ban TikTok (for the same reason that US is banning TikTok now). US and India are not really rivals and US can retaliate against India if US companies are blocked so math is that it's not worth it to block for now but it can change in future.

Most other countries are not capable/do not have economy and critical number of people to have viable clone of social media. They block social media from time to time during elections, etc.