What are the requirements for the PC if I want to record in good quality with OBS Fortnite?
Depends on the settings and the graphics card.
If Fortnite runs smoothly, the PC should do it too
I would minimal take a ryzen 3 1200 with RX 570 / GTX 1050 TI
But I would recommend a Ryzen 5 2600
I think with older processors and graphics cards is synonymous, depends on how your PC looks / should look like