For completeness here goes the best steelman against GrapheneOS’ abstention I could summarize. Am I missing any other considerations because this is not strong:

Despite age verification laws empirically not working (VPN use just skyrockets), Rawls would argue that civil disobedience requires visibility and the acceptance of associated consequences. Anonymously non-complying against a democratically enacted US law lacks this structure. This makes it more akin to evasion, which doesn’t mean it’s necessarily wrong, it just weakens its high ground status.