Why is UBI a state thing? From a thought perspective: This could also be arranged outside a centralised state? The best case would be, it becomes culture to support those we need it, but that is not too practical these days :)
Any other system or systems that you have in mind to combat the inevitability many peeps on earth will not be able to find a paying job, since the numbers of such jobs will decrease over time next few decades, whilst the world population will increase a lot, like a factor of 2 maybe even 3?