Personally I favor a UBI but I think it needs an intellectual basis, i.e. I am not for "stealing from the rich". Perhaps part of this intellectual basis could consist of an appreciation that natural resources are not distributed equally.
Do we? Some people might believe it but there doesn't seem to a lot of evidence for it yet. If anything it seems that it might behave like other seasonal viruses such as the flu and especially like other coronaviruses such as the common cold. That is it might mutate so rapidly that immunity will not last.
So we might have to live with it or something like it for ever.
If you just took all the existing taxes and welfare programmes, carefully noted what net payment people are getting at various income levels, and then replaced it with a simpler system of a fixed UBI payment and a tax system to roughly replicated the same net payments; I don't see how that would be any less sustainable than what we currently have?
And current systems have been muddling through in most countries for quite a while so far.
However, if by UBI you mean that everyone is supposed to get some extra magic money out of nowhere, yes, that wouldn't really work.
The thing about UBI is that it in no way, shape or form, prevents people from doing whatever is needed or profitable.
There are a number of people which have sufficient funds to live off $1000 a month and they continue to work. Heck, even the bloggers who talk up such schemes are still producing something of value to the society.
Humans like to work, just not necessarily for a boss. A UBI removes any disincentive from working and allows you to keep what you make except for the tax rate unlike welfare which taxes income at 100% . It allows you to be creative. Right now, we are ignoring the contributions of millions, if not billions of people because they are kept at the edge of survival. Imagine if we created a world that allowed all the billions of the world to contribute imaginatively, cooperatively, and productively. That is what UBI promises, but it does require faith and trust in humanity (read Rutger Bregman's Humankind book for a primer as to how to shed the lies we've been told about human nature).
As for hard maintenance of systems, that will probably cost more to pay people to do it, but it seems very reasonable to reward essential hard work more than we do now.
One final thought. What do you expect you or others you know would do if you had $1000 a month per person in your family given? Maybe some would want to sit around for decades doing nothing, but that personally sounds like an awful life to me and I suspect most would agree.