UBI can't increase inflation - ever. It's not adding money to the economy, it's redistributing what already exists.
It's not the same thing as just giving everyone a million bucks. UBI is essentially a reformation of pre-existing welfare that gets rid of all the overhead and administrative costs involved in deciding who gets what.
Taxpayers on the high end (the upper 20% certainly) are paying tens of thousands, even hundreds of thousands or millions of dollars in taxes. They avoid what they can, but they still pay a lot. These people will get say, $800/mo back from the government. It's a pittance to them, and doesn't offset their taxes whatsoever.
Meanwhile someone making less than $10,000/year, is now doubling that to almost $20,000. That's HUGE for them.
UBI is, in essence, a redistribution of money from those who pay the highest taxes to those who pay the least, and it's done without even increasing taxes. Been a long time coming, to be quite honest.
More importantly, doubling the income of people in the lower income brackets is going to massively increase consumer spending. This is the connection that finally completes the circuit on the flow of money in our economies. Right now it's just been accumulating in the coffers of the very rich, being invested and re-invested in ways that always gain and never lose them money, which has resulted in stagnation across the western world.
Increased consumer spending will also come on top of and out of, increased wages that will result when people aren't faced with a reality of work for a pittance or die, and can now actually negotiate fair wages for themselves from a position of financial security.
The biggest winners in UBI economies are the lower and middle classes, but there are no actual losers in a UBI economy. Even the ultra-rich who are most effected by taxation, are going to see their investments and businesses increasing in profits due to the explosion in consumer spending. The only real issue is overcoming everyone's preconceived notions of what UBI is and does - like this idea that it increases inflation because people now have more money to spend. It might be more apt to say that UBI will 'simply' massively increase the velocity of money in the economy.
With that said, there's a fair number of the ultra-rich who seem to think the masses deserve to wallow in misery - it's not enough that they win, everyone else also has to lose. UBI won't be able to fix that, and these types will be the ones hardest to overcome in regards to implementation of UBI, because they have the wealth necessary to fight it to the death.
Right now, the solution our "elites" have come up with to offset our unsustainable stagnating economic systems, is to import foreigners to continue massive economic growth: More people to tax, more loans to give out, more debt to add to GDP "growth", and lower wages across the board to save money. It's the wrong approach because they aren't considering most of the actual social/economic costs doing this. As such, I'm not particularly concerned about all this for the future of humanity - in the long run something like a UBI will be implemented regardless. The alternatives are completely unworkable and will result in collapse or at least greatly reduced economic efficiency; while UBI achieves the opposite, both with increased velocity of money and allowing the economy to continue to function while it is further automated.
The nations that implement UBI-like systems will succeed, and the ones who don't will fail. The actual choice we're faced with in the near future here, isn't whether or not we should implement a system like UBI, but whether we'll put it off until after economic collapse, political/social instability, and civil unrest/war, or before.
Knowing humanity, we're definitely going to kill each other a bunch first.