The solution to this is simple, in my mind. The teams should tell the players if they don’t want to participate in the National Anthem to stay in the locker room until it’s over. Employers should not be obligated to provide a platform for public protests.
That would be one way to solve the issue of conscientious objectors. Do it indoors all they please, but anyone who wants to salute can come out ahead of time. Their choice, but it ain’t a protest field, it’s a football field.