It doesn't work in both directions though. That Trump isn't allowed to block people on a private website he (effectively) uses for official business is not equi

It doesn't work in both directions though. That Trump isn't allowed to block people on a private website he (effectively) uses for official business is not equivalent to that private website being required to facilitate his official business. The first amendment prevents him from blocking because it would suppress the right of the population to address their officials, but it would also support their right to deplatform him as an exercise of Twitter's free speech.