Is that a good composition in 2020 for 700 euro?

Intel® Core ™ i5-9400F
2 x 8 GB RAM
GeForce® GTX 1650 4gb
Intel® B360 mainboard

For e.g. Fortnite, csgo, gta 5, etc.

You can do that.

If you were using an AMD CPU you would have had more money and a better GPU.

In principle, you can do that.

I will look around again thank you

Rather go on AMD basis is simply better in terms of price performance but is your decision and I would not get a GTX 1650 4GB, because the 4GB are enough for some games in 2020 but in the future you will not have a chance with newer games with 4GB

Prefer a Radeon RX580 or something with 8GB

No - for the price this is not a good combination. A better graphics card and processor should be possible.

https://hardwarerat.de/...a-ssd?c=78

Take the Ryzen 5 3600 as CPU

and as a GPU the RTX 2060