I'm looking for a gaming notebook for 300-400 euro with which you can play Fortnite.
You will not find a gaming laptop with the money, but you may also be able to play Fortnite on low graphics settings on a normal laptop
Fornite is not really a PC job.
Take a good used one from Ebay. 8 GB Ram, custom graphics, 17 inches
No, there you have to put more than twice on the table. Even with stand PCs it is priced (at 400 euro) very scarce. Or you'll get a console right away.