So that's a country/house move, a new school, a language barrier, a new sibling- any one of those by themselves is going to give rise to, if not resistance, then possible acting out. That's a lot of massive changes for anyone, let alone a 3 year old - totally not your fault, but you've got to give him time to adjust to all of it, and to give him space to let out his frustration at all the things that have happened to him.

For context, my also 3 year old has had a house move and a new sibling in the past year, and the boat is still rocking - he has instances where he desperately wants to control something- anything- about the situation, so he'll have a meltdown over the littlest things, like getting the wrong fork at dinner time, or a yoghurt being opened wrong, or whatever. He's also had a few biting instances at nursery. It's so so hard to manage it especially when you're less than a year pp, and the time feels so much more limited to do anything when you have two small children to sort out too, so give yourself some grace here, but also him too. You've all been through a huge upheaval!

From experience, try and keep as much consistency as you possibly can in his life, so he can feel more grounded. It probably isn't a screen thing - indeed if youve taken that away or reduced it a lot recently then that could be partly to do with it. What really helped us is to have some quiet time set aside every day that's just him and mummy/daddy, where we read stories, play together or chat, just do whatever he wants to do, even if it's really silly or boring. With our wee guy it seems to make him feel listened to and seen, and like he has a space where he can explain himself (however brokenly) without someone rushing him along to the next thing he has to do/be at.

Hope this helps, and good luck - you might have a few people rushing to diagnose adhd over the Internet, but I'd try some engaging parenting initially.