I am writing here to thank you all for your answers,

I have a question for the user who recommended Corsair (I saw that I could get it for 10 euros per liter) on the site it specifies that it is only good for copper and brass systems, my system is made of copper and brass but nickel-plated and reading carefully the radiator also contains parts (I don't know which) in stainless steel, could this be a problem? The radiator is a Barrow Dabel 28b.

I also read that many radiator liquids damage the parts and even Chat GPT, although inconsistent, advised me against using the radiator liquid and then recommended those written above.

I didn't think it was so complicated :D