The Netherlands: a limit that moves with what you earn
The Dutch limit is the one here that moves most explicitly with what you earn, published as a table rather than as a single figure. NIBUD publishes financieringslastpercentages each year and the Tijdelijke regeling hypothecair krediet gives them force: they set the maximum share of gross income that may go to a mortgage, running from roughly 22% at low incomes to roughly 28% at high ones, and the percentage moves with the mortgage interest rate as well as with income. Earning more does not merely raise the ceiling in euros, it raises the percentage too, until it flattens out at the top of the table.
The reasoning behind the sliding scale is that a household's unavoidable costs do not scale with income. Somebody on a modest salary needs a larger share of it for the essentials, so a smaller share is available for a mortgage; somebody on a high salary can commit proportionally more without running out of money for groceries. This page uses 28%, the upper end of that band.
Because the rule is written against the mortgage, other debts do not so much fail the ratio as shrink the amount you may borrow: registered consumer credit reduces the maximum a Dutch lender will advance, and the BKR credit register makes it visible whether you declare it or not.
Income is assessed before tax. And because the tables are republished every year, a maximum quoted last year is not the maximum this year: the percentage that applied to your salary in one year can move in the next without your circumstances changing at all.