believing the 2020 election for POTUS was rigged is not a crime
That's exactly what Jack Smith said. Read the indictment!
what he is accused of is "acting" on his beliefs
What he acted on was illegal. That's the point! In this country, you go through the courts, which he did and lost 60 times. Al Gore went through the courts and accepted their decision even though after all the votes were counted in FL, it was determined he won. He didn't incite an insurrection.