Your mom sounds like a desperately unhappy woman who has lost any sense that she can actively change her lot. She seems to be convinced that any effort to change things will fail so why bother? Since she feels so helpless to improve herself (put herself up), she puts other people down. She can then feel a little better without having to make any effort herself. Ultimately, she knows it’s a sham, which only makes her feel worse. I suspect she meets the criteria for a depression, but I’d need to talk to her to be sure.
The best thing you can do at this point is try to get your parents to see a marriage counselor. Do the research. Find out which local therapists are taking new clients, which ones take your family’s insurance, and whether there are therapists who will start online while the pandemic continues to prevent office visits.
Give your folks the information. Tell them how much you love them and how important it is that they get the help they need to be happier. Stay compassionate with them both. Don’t fight with either of them. (It won’t help.) Do repeat that they need more help than you can give them. Lovingly, persistently, urge them to take care of themselves by seeing someone who can help.
I hope you are focusing on getting on with your own life. At 24, it’s time.
I wish you well.