I am pragmatic, not a purist. Having more people (refugees, starving artists etc.) receiving money from benefactors is better than less.
That means spreading the wealth redistribution as thinly as possible: one person one account (it is also good for voting).
We can approach such a system by kicking out the artists who already got 100 donors, and forcing them “off the market” the same way someone should leave a dating site when they paired off.
The problem is that various actors have incentives create fake accounts. It isn’t even so much about UBI for people being unsustainable, but that people can create fake accounts (sybil attacks). There HAS to be a gatekeeping mechanism. There has to be a condition, the U can’t stand for Unconditional. It can stand for Universal (to all members of a community).
The hard part is ensuring there is no serious corruption in the mechanisms that whitelist accounts. WorldCoin scans eyeballs and Proof of Humanity does network analysis and tokenomics. I think that there should be a self-regulating organization (SRO like FINRA is for example) of KYC providers that stake a surety bond proportional to how many accounts they whitelist, and if some duplicates or fake accounts can be proven, in some sort of due process, they lose that stake. So they have some enforcement.
But still it may not be enough, for example for a national election there are strong incentives to register fake voters, and if the whole thing is done without appearing in person then that’s even easier to do. So then you need really harsh penalties for corrupt bureaucrats and ways to revoke certifications. But by that time some amount of UBI / welfare / disability benefits will have been paid out, or an election to install a director or head fo state has already taken place.
Far better not to concentrate the wealth and power to begin with, because then there would be less incentive to cheat and rally and grab the spoils of “war” whether that is marauders raiding a village, or a political party taking over an election, or Jeff Bezos now picking winners and losers in his investments / philanthropy
Basically, it is not that UBI is unsustainable, but that free (or subsidized, by exceeding the value whatever contribution the recipient makes to the system) money requires some increasingly harsh mechanisms to vet people.
At the end of the day though, we need such systems as there is a growing proportion of people whose labor just simply isn’t valuable enough to exceed their cost of living. And asking them to forego the modern conveniences of life, like safe potable running water and at least 500 square feet of space to live in, safe neighborhoods, access to lifesaving emergency medicine etc. is silly. If we subdidizs them anyway, why not standardize the system and remove corruption?