How much ram minecraft assign?

How much ram should I assign to minecraft, have 8gb and want to play with shaders?

Always half, so 4.

Is there a reason for this?

I don't know, that's the "rule".

You could also allocate 6GB, then other programs have to cope with less

Then I find your answer less helpful. I thought there was a reason for "always".

So that the other programs still have enough, as I said, you could also assign 6GB, but then you should do without other background programs (Google, Discord, etc.)

But why half then, when I have 32 GB available, for example, and my background programs only need 4 GB?

Yes, you are right, with a higher RAM the whole thing no longer counts, please forgive me.