It's pretty much all laid out on Wikipedia.
He initially supported the Democratic Party but because of crypto and AI he donated millions to super PACs for Trump, supported DOGE and said that children are now being readicalized to hate capitalism as well as directly messaging the Trump administration to put pressure on Universities like NSF, SU and MIT because of DEI or something like that.
https://en.wikipedia.org/wiki/Marc_Andreessen#Political_view...
Is he wrong? The mayor of NYC is a socialist elected by young voters.
One can support a party and then change to not supporting a party for a variety of reasons. Such as disagreeing with the direction the party is going, especially locally, or even as simple as eschewing the previously supported party because you are betting the other one will win and need to curry favor.