No one's taking this negatively, they're just saying to just go for it. Realistically, you have nothing to lose by posting whatever you want, especially because you're remaining anonymous. I know it'll be difficult, but you have to set aside your anxieties, approach this from a whole new mindset when you post from your new accounts. This is your chance to express yourself creatively without having to worry about others' opinion.
You're right in that not everyone is going to like what you make, but that doesn't matter so long as you find joy in what you make. I've been writing online for ages so I understand that criticism can be hard to handle at the start, but you'll never get over that anxiety you feel if you just overthink it. You have to take that initial leap to get going.
Maybe try making something, art or writing, it doesn't matter as long as it's something you want to make. If it helps, use something you've already made but weren't planning to post online, or just make something without thinking of posting it, then schedule it to be posted at a time when you're asleep. When you wake up, it'll be there and you'll have taken that first step.
Honestly, I think you just need to do whatever you want to do. Don't overthink it. Everyone who posts online comes across people who dislike their work, but we also find a lot of people who love it and connect with what we create. Your creativity is valuable and something that can bring joy to others.
