if you say anything in support of palestine
You can say stuff in support of Palestine just fine.
You can't be in support of abspecific group called Palestine Action because they've been designated a terrorist organisation. Whether that group warrants being defined as a terrorist group based on what they've done so far (obviously there could be intelligence that the public aren't privy to) is dubious.
Or just support a different group that is calling for freedom for Palestine but hasn't broken into a military air base and vandalised some planes.
A lot of the people that have been arrested aren't protesting in for Palestine alone, they're protesting that that specific organisation shouldn't be considered terrorism and the overreach of the law that has been used. Their whole intention was to be arrested. That was the protest.