I asked him what he wanted me to do and he said get rid of everything a la Marie Kondo 🙄
I feel a little bit sick and I'm hiding upstairs in our room feeding the baby.
My dad used to go on these "cleaning rages" where he'd rip up and throw away loads of things so I'm feeling a little bit triggered by my partner's rage cleaning. To be clear he's not shouting or aggressive or anything.
Don't be afraid to remind him that housework isn't just your job, it's both of yours. Maternity leave is for recovering from birth and looking after baby, not for running yourself ragged and setting a precedent that all household related tasks are yours and he "helps you" if he feels like it. If you are afraid to raise this issue with him for fear of his response then you have far bigger problems in your relationship than a bit of clutter.
Go on YouTube, find Hoarder's Heart and show him the video where she talks about this very thing you've mentioned above. If you are forced to de-hoard all of a sudden it retraumatises you and you might respond by hoarding worse than ever before.
You're decluttering, you're doing it, he needs to be patient. Although unless you need the money you could donate rather than sell, to speed things up a bit. Selling is not only time consuming waiting for a buyer but in listing the stuff and answering questions, as well as sending sold items off, so it means less time for housework or having fun. What's more important, your marriage or the few hundred pounds you'll make selling it all?
He needs to stop blaming you though. You haven't pretended to be something you're not and he could see the way you were/lived before you had a baby. The pair of you are where you are and nobody forced him there at gunpoint.
If the place is a state he needs to look around it and see what he can do to make it better eg put laundry away or buy a new Hoover, then he needs to go do it. He has a child now, his evenings aren't his any more, just as your evenings aren't yours, it's family time and he needs to get on board with that, otherwise you may as well be a single parent.