I wanted to know if this ready-made PC can consistently achieve 144fps in Fortnite. (1080p, low settings, performance mode)
144 probably less, but solid 60 are possible in any case. You can't expect 144 FPS from a 500 euro PC either, for the money this is probably one of the best options that are available to you in the new state, because you can easily upgrade a mid-range GPU later.
With luck you will get 50 xD
The part doesn't even have a graphics card, just a graphics chip.
Don't think the PC doesn't even have a dedicated graphics card. You can be happy when games are running at all.