Which components for PC?

Since my laptop is starting to run out, I now plan to build a PC myself, together with my cousin, who knows about it. Now my question to you is which graphics card and which processor you could recommend to me. I want to use the PC primarily as an office PC, but as a good one! It shouldn't load long and respond quickly. However, I also want to be able to continue playing my games. They all have no high requirements, except for GTA V, which I recently got. It doesn't work well on my laptop, which is also a reason why I decided on a new PC.

I thank you now and I look forward to your answers!

Together with my cousin, who knows about it. Now my question to you is which graphics card and which processor you could recommend to me

Your cousin should then be able to answer you.

Would recommend a Ryzen 5 1600 and an RX 580 as CPU / GPU combination.

For office you can use almost anything that has 4 cores, but that's not enough for playing.
I would take a Ryzen 5 1600AF (12 nm) and an AMD Radeon RX 580, that's enough for GTA V, plus an AM4 B450 motherboard, which are currently in demand from MSI.

Not necessarily. Having knowledge of PC assembly and knowledge of which hardware is currently the most worthwhile differ are different.

For example, I can also build a PC (I've even built several), but at the moment I'm not very well informed about the good & worthwhile hardware (because I don't need a new PC at the moment).

If you want an office PC with virtually no loading times, an Mvme hard drive is a good place to start.

In order to do justice to the game Gta, but not to spend a lot of money, I would take a Ryzen 5 2600 in combination with a gtx 1050 Ti as Gbu as Cpu.

If you can / want to spend a little more money, get the Ryzen 5 2600 or 2600x.

But no 1050TI, it was hit against the wall by the same expensive RX 570 when it was released…

I personally am an Nvidea fan. It's his business

Specifically, you need a PC with around 500 euro for your requirements:

https://geizhals.de/...WL-1002498

An R5 1600AF has the CPU power of an R5 2600, unbeatable for the price.
The RX 570 is also enough for GTA 5, a few details don't stop at MAX:

https://www.computerbase.de/2020-03/gta-v-benchmark-test/#abschnitt_benchmarks_in_full_hd_ueber_alle_klassen

Then there's the screen, keyboard, mouse, headset…

What kind of budget do you have? In principle, an APU should be sufficient for your purposes. The Ryzen 5 3400G would be something.
What would be better would be an AMD Ryzen 5 1600AF in combination with an RX 570.

I would like to spend a total of not more than 250, at most 300 euro for the entire PC (without mouse, screen, etc.)

Then it will run out of something here:

https://www.hardwaredealz.com/bester-gaming-pc-fuer-unter-300-euro-gamer-pc-bis-300-euro/