Administration and enforcement are WAY higher when giving something to 100 million people than when giving it to 1 million.

At least where I live calculating someone's income is trivial. Government have that data. With GMI 1 million people would need to say to the government that they want the money in a particular bank account, and the government would need to deal with ensure that petitions are legit. With UBI that work gets multiplied by a hundred or more. Suddenly the government has to control that the money is going to the proper bank accounts. And has to deal with WAY more fringe cases (recently deceased, minors, double identities, etc). There's no case for UBI being easier to manage.

As for the rest the problem is the same between UBI and GMI if you think it through. UBI would need an humongous budget. Where that money will come from? Two options, printed or taxes.

Printed is out of the question, hyper-inflation would be for the history books. Taxes would mean that most people end up loosing as much as they are gaining. And at the end you end with the same dilemma people who after taxes get the money and people who not. Just that it gets decided by tax brackets.

And the fundamental issue is the same. Giving that the basic income is actually what's needed for a living... That would be pretty similar to the most common income for a job. As that's how economy work. Money is just an exchange for people's work. So the most common salary is more likely to be very similar to the amount of work needed for sustaining a population divided between the working population. I don't see it working on the proposed way, of UBI being a livable wage and the minimum salary being able to add another livable wage on top of that. I don't see how that would even be possible. Most likely on that scenario UBI+minimum wage ends up becoming what's needed to actually live good. And UBI alone becomes unlivable, making people who depended on that poor again.

Not that GMI solves many issues. Just simpler to get a pretty similar outcome.

Still I think both are bad approaches. Because they make it possible to some people to live without working(people that can work), out of others work. That will always make frictions.

My approach would be just for the government to give jobs instead of money, guarantee jobs with livable income. Or if not all that much work is required for society, then lowering the working hours from 40 to less until all working population could share the load. I don't buy a society where some people work and others don't (that's why I don't like capitalism). I prefer societies where everyone who can work do actually work until society needs are filled.

Yeah, you got the point right. "Monotonicity" is important. That means, if somebody puts in more effort, they should get out more of it.

x-axis is how much you earn from jobs, y-axis is how much you take home in-total.

The only thing that remains to be determined is the parameters of that curve (offset + slope). A steeper slope would mean people are more motivated to go to work, but also less tax income for the state.

I would propose a slope of 1/2 and an offset that is big enough to be able to live on it, but i believe this is something the people will have to determine through voting.