Is this laptop good for school / home office with a bit of surfing and etc?

https://www.hihonor.com/germany/product/honor-magicbook-14

A very good and powerful device for school, if your budget allows it, it's good.

Is it also so good for watching youtube or netflix or twitch etc? Surf in general? Multitasking?

If so, he should be able to do that, is an all-rounder, so to speak

If you want to be on the safe side and it is within the budget, you can take the variant with 16GB Ram and 512GB storage, but even if you take one of the other variants, YouTube, Twitch etc. Are certainly no problem. You will probably not be able to edit videos with this PC.