18F I want to be less difficult to please. How can I do this?

I don’t like myself very much and my mother keeps trying to help me out by giving me clothes to wear and doing my hair for me. She spends literal hours helping me and whilst I’m very appreciative, I’m never happy with my appearance. She says I’m starting to sound unappreciative and if I continue like this I’ll drive people away because I’m such a buzzkill when it comes to everything. I do try to be positive, but it just feels like I’m lying and she can tell I’m lying and it only makes both of us feel worse.

I’ve started smiling more when I receive gifts, whenever people cook food I eat it even if I don’t like it. Although I’d say my outwards appearance is fine, on the inside I’m still very difficult to please and I genuinely have no idea how I’m supposed to get better at that, especially because I don’t know what I’m looking for exactly — I just feel generally unsatisfied. Is it just a “fake it till you make it” situation or am I missing something? I thought for a while I might have low self esteem but I think the issue is that my self esteem is so high and it means my impossible expectations are never met.

I should add that I’m slightly mentally disabled which makes me more childish than other people my age, and is probably a causing factor of this.

TL;DR: People are getting upset with me because I’m never satisfied. How can I learn to accept that I can’t be satisfied and change my outlook?