context:

Normally social networks have rules and guidelines that prevent you from posting or commenting on something inappropriate but Twitter doesn't have that, so Federal Supreme Court Minister Alexandre de Moraes told Elon Musk to fix it and he refused

social networks have a representative from each country working on them, when Alexandre de Moraes asked Elon Musk to take control of Twitter, Elon Musk fired all Brazilian representatives

Alexandre de Moraes said that Elon Musk had 24 hours to present a Brazilian representative, Elon Musk didn't do that so Moraes banned Twitter from Brazil

and what does miku have to do with this?

Some people were angry with Moraes for banning Twitter so they went to protest, and someone put the Brazilian miku on a poster saying "free miku, Moraes out"