Just good, solid, relationship advice that applies to both personal and professional relationships is to not get involved with people who badmouth their current or former employer/partner. You are just setting yourself up to be the next person they are publicly badmouthing.

If I want to vent about an employer, I don't name them on a globally available platform. It's unprofessional. If they did that to you, you could sue them.

This is a reason why, "Why are you leaving your current job" is a common interview question. You get minus points for badmouthing your current job.