The Posse Comitatus Act is a law. However all laws are the agreements that form the architecture of the state.
https://calmatters.org/justice/2025/09/trump-national-guard-posse-comitatus/
Trump has already broken Comitatus once, however what's happening in the California courts can absolutely give the National Guard the ability to refuse legal orders as it's currently being legislated. https://nlgmltf.org/military-law/2025/faq-on-refusing-illegal-orders/
The US is scary right now. Talk to your neighbors, build community and if that's not possible where you are let me know. I'm happy to try to point you in the direction of those you can organize with. Our only safety is in numbers, our greatest weapon is solidarity.