Overwhelmed in my 1 bedroom apartment and don’t know where to start. Advice? Tips?

I'd prioritize the kitchen. Gingerly pick through the shit you're most willing to throw out without cleaning or sorting and then revaluate. Or set a five minute timer to throw things away and just do it for just those five minutes. Get rid of anything spoiling or that smells bad. Move FAST, do not try to be overly ambitious at the first pass, and go take a break to stand outside, away from the clutter, and breathe.

take breaks. eat snacks!

Also you need to get your mom to stop bringing you shit somehow. Try telling her that if she gives it to you, you WILL put it in the trash, doesn't matter if it's totally new or usable or whatever. She's pushing her hoarding behavior on to you and using you as storage/spillover. If you follow through a few times the anxiety of stuff getting thrown out should start to outweigh her confidence that she can guilt/bully you into keeping trash around.

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