But if I were to work for a remote-first company, I'd expect them to pay a stipend on top of my wage, equivalent to the amount of money they save by not having office space. A quick Google indicates office space costs about $500-$650 a month per person (in Amsterdam, according to Google's summarized results from instantoffices.com), or between 150 and 450 euros / month per m². With that money, as an individual, you could also afford a spot in a co-working space if need be.
I think a $500 or €500 / month stipend or reward for working from home is fair; it's a decent amount of money, and I'm pretty confident it's still cheaper than renting an office - you don't just save on rent, but personnel as well, and things like support and maintenance contracts on the utilities, coffee machines, etc.