Possible bug? sim keep saying this is inappropriate

That doesn’t sound right. I’d report that on Answers HQ if I were you.

they made it like that in a patch a long time ago not sure why, the always welcome reward trait fixes that if you're fine with cheats you can cheat the 500 points to get it
testingcheats on or true I think works too
sims.give_satisfaction_points 500
Try the second with and without the space I think it works both ways not sure now I always type it the same way.

DO you control both sims? Or are you over at the sims house that you don't control? Or are you at your sims house?

if you're visiting the house of a sim you don't control and cook them a meal they say it's inappropriate for a guest to take food no matter how good the relationship bar is. I guess the sim thinks you're stealing their food???

the always welcome reward should stop that from happening.

I don’t know if it’s an actual bug, but it’s annoying. Even when you go to family members houses it does this.

I think I read somewhere that only best friends and sims who are engaged to each other have permission to do that without the always welcome reward. It's been like that since the beginning of the game.
I can't confirm from personal experience though, as I usually give the always welcome reward to sims who visit other houses often.

I read somewhere that it is intentional now, to be honest i am quite offended when someone so close to my sim (aka his family) is yelling at him for cooking a meal or sleeping in his old room, I used mods to make my sims do everything he can without the house owner consent, because cheating and buying always welcome trait is getting old, I believe there is a version that only allow friend or family but not stranger.

Thanks for the information guys. I don't control the other sim. He was visiting his girlfriend at her house at max relationship status excluding engaged and married. He just wanted to be kind and make some breakfast for the both of them, then she started yelling and saying it was inappropriate. Eventually, she yelled at him one last time and told him to leave... :( I guess I'll use some trait points and get that Always Welcome trait.

There is an actual bug in which Sims who live in the same household will tell each other that showering, cooking or sleeping is inappropriate. I had one mother who kept waking up her own toddler to tell her that sleeping in her (the toddler's) bed was inappropriate. It happened to me when I had a family vacationing in Granite Falls and they all went to visit the Hermit. When they returned to the house, the first one back apparently decided that she wanted to live alone. She almost got her wish... .

I spent a holiday at my non played family's house and tried to cook a grand meal for everyone. Yeah, got yelled at :D It was a custom holiday too, to celebrate families/legacy and being together with the family.

I believe it's cooking, sleeping in a bed, showering or bathing, and repairing stuff that triggers the inappropriate interaction.