Fine, I'll indulge you.

white isn't a race it's the social construct

This is both true and false. By all accepted definitions of race that I could find, white counts as a race. However, race as a concept is a social construct. Some folks back in the day decided to categorize people by things they have in common. (e.g. physical attributes, geographic location, genetics) However, this doesn't have any basis in science due to there being more genetic variation within the defined races than between them. Most biologists and anthropologists don't accept race as a scientifically valid biological classification.

that means the absence of race This is false by all definitions of race. Race is just a collection of people sharing similar attributes, so the "white" race absolutely counts, considering all "white" people share a similar characteristic: skin color.

Irish stopped being a race when they were accepted into whiteness by becoming police in large number This one threw me for a loop, as I'm not really sure what you mean by this. Irish is 100% still a race, as they are a group of people that can be defined by geographic location. There are groups that don't think they belong in the greater "white" race due to some historical beefs, but at the end of the day, most definitions of the "white" race include Irish folks, as they have white skin.

That's why it's literally impossible to be racist against white people This part doesn't make sense. By the most common definitions of racist, it's possible to be racist against any given race. Some definitions of racist that I read in school did change that by adding a clause for racism being prejudice towards a marginalized group. In that case, it wouldn't be possible to be racist towards the greater "white" race, as they have never historically been marginalised. However, this definition of racist hasn't been widely accepted, as it almost exists to prevent being able to say racism towards the "white" race exists.

If you think that it's impossible to be racist towards a race that is all-encompassing like the "white" race, then, unless you're using a different definition of racist, then if would be equally impossible to be racist towards the all-encompassing "black" race.

No need to lash out just because people are calling you out for your misunderstanding of your own words. Given how your sentences are written, English might not be your first language, so there's a good chance that this misunderstanding comes from a translation or language barrier. Hopefully I have cleared things up!