Kind of works if the income groups are based on percentiles, but it doesn't say so we don't know if this is behavioural change or just a growing middle class.

Yeah, that's true. Really, any kind of area graph just isn't the way to go for this. It just looks prettier than anything sensible like a bar graph or box plot.

Since immigrants are net contributors, yes it will.

It think it is normalised for inflation. It says in tiny text in the corner that it's adjusted to 2023 USD. Could be clearer though.

I think showing an average per year for each decade would have made more sense than a total, otherwise you can't really compare 3 years of the 2020s against 10 years for all the others.