Do you have any info on his background with the breeder?
Was the kitten raised in the breeder's home?
Was he handled much? Did the breeder play with him?
😖But I don't know if I should try to pick him up, stroke him or get him out of his hiding spot😬
On that point—absolutely not! It’s only been three days; if I were you, I wouldn't force him.
He’s only just been taken away from his mum and the rest of the litter, and he’s arrived in an unfamiliar place with one or more strangers, so it’s perfectly normal that he's a bit unsettled. What matters right now is that he’s eating and drinking. He’s found himself a little den; perhaps you could offer him a better-placed one, but the best approach for now is to just ignore him.
Go about your business as usual, but of course, keep feeding him—not necessarily in your loo! 😂 But there’s a good chance that to begin with, he’ll only come out to eat at night. It’s important that you use the same food he was getting at the breeder’s.
If it's dry food, it’s a good idea to give the bag a good shake and let the kibble drop noisily into the bowl, while saying his name as you fill it.
If it’s wet food, do the same—don’t hesitate to rustle the pouch or packet before serving so he associates the sound with food and your voice.
You could also try offering him treats like The Laughing Cow or some cream cheese, which cats usually love, but avoid milk unless it’s lactose-free.
Let him explore his surroundings without staring at him and be patient. He should gradually start coming towards you, and since he doesn't seem to have a troubled past, it should happen fairly quickly—probably in less than two weeks.
😯Some people are telling me to pick him up anyway despite how he reacts, otherwise he’ll never come to me and he’ll go feral🙄
Now, that’s risky and a bit of a double-edged sword. It all depends on the breeder; if he was handled from a very young age, it might actually help clear the air, but it could also do the opposite—even if only temporarily 😯. There’d be a risk of a short-term setback.
He won't "become" feral unless he was already feral to begin with, and if that were the case, you definitely shouldn't force him as you’d risk terrifying him for the long term. To me, he just sounds scared because of the change in environment and people, but he’s not a feral kitten.
As for the "aggressive" behaviour, it’s all just bluster. You need to respect his anxiety, but don’t be afraid of him or think it’s a bad sign—it’s just normal.
The kitten will probably be most active at night.
For now, you just have to wait for him to make the first move.
You can also try leaving the house for a bit so he can explore his new home while you're out.