I'll not be snarky and say with some certainty that mathematicians teaching mathematics is important to the field of mathematics.

Maybe some sort of new enrollment/payment system, like the religious practice of giving to your church a % of your income... The same could be done in a UBI society.

Because the amount of UBI in dollars received will change over time, expressing it as a percent will work. Let's call it UBIC or UBI-Cent for 1/100 of your UBI. Maybe a fully pledged 100/100 UBI would be UBID or UBI-Dollar.

Let's say you have a platform for teaching and learning, and students subscribe to their teachers and peers by literally pledging their UBIC to them.

Within this system, students have a means to live and study using their UBI, and teachers the same. Imagine liking the work your friend is doing, so you pledge them 1 UBIC. Or finding a teacher with a good price to match your situation.

I feel like there is room for entirely new systems of teaching/learning in a society where everyone has their minimum financial requirements fulfilled and is not going to starve.

Sure, at the expense of the next generation of mathematicians who may not have anyone to teach them.

Ubi is a non realistic utopia to begin with (offsetting the temperature scale doesn’t make anyone any warmer).

But even if not - no.

The best scientific breakthroughs were always made because of some scarcity and urgent necessity. Check Turing, history of Xerox lab etc etc.

Laziness and easy life is a bad motivator. Whether you like it or not.

I mean, if they were unemployed, they wouldn't be mathematicians anymore