Nobody negotiates net. It's not even practical.
Your tax situation will depend of the other revenues you might receive on top of your wages and the deductions you are eligible to and your employer doesn't have to know about that.
Nobody negotiates net, but companies will keep in mind an employee's lowest possible tax bracket given their gross (and therefore their highest possible net) when determining the cost:benefit of offering marginal "material compensation" increases (vs other components of total compensation) — both during initial negotiation, and when trying to design later incentives.
Which is to say, if you're making USD$100k/yr working for Ericsson in Sweden (where you're in the highest, 52.9%, tax bracket for any marginal income above USD$83k), they're gonna be thinking differently about how to reward you as a high performer, vs if you were making USD$100k/yr at Google in the US (where that salary would instead just have you scraping the top of the 22% tax bracket.)
Google would almost certainly just give you more money — and would likely continue to do that indefinitely, as even the highest US federal tax bracket (37% at USD$600k/yr) isn't too onerous. Ericsson, on the other hand, might already rather offer you something non-monetary and "cheap" for them (e.g. a company car), rather than biting the bullet on a "substantial, productivity-incentivizing" raise (i.e. one that meaningfully increases your net income.)
And that is why precisely why salaries tend to be lower in many European countries (that have these high tax brackets); and why everyone in those countries instead expects / demands / enshrines requirements in law for tons of non-monetary benefits, like long vacations! "Purely salary" and "salary levels off, then tons of non-material benefits" are both Nash equilibria in compensation space; just very different ones.
To begin with, non monetary benefits have to be declared in most European countries and impact your tax rates and are taxed the same way than giving you more money so your whole dodgy reasoning immediately falls apart.
The only time I've heard of negotiating net is in certain Gulf countries where employers will pay all your taxes for you. Not a thing in the US or Europe though.
Nobody negotiates net. It's not even practical. Your tax situation will depend of the other revenues you might receive on top of your wages and the deductions you are eligible to and your employer doesn't have to know about that.