Cash just about never sits just around as long as whoever holds onto it has no current need for extremely liquid assets. Like insurances.
I doubt that the ratio of cash that ends up bound up that way to the one that doesn't changes a lot overall.
The real problem to UBI is governments creating income via debt, IMO.
The national debt is just a hidden tax on future generations. You're stealing resources from the future (by selling claims to them in advance, that's what national debt is) and spending them in the present. It's justifiable in extreme cases like a war (or perhaps for massive public investments that can't be funded within the existing budget - which is actually not that common), but really not otherwise.
The reason why the debt keeps growing endlessly is that there is a 0% lower bound on the interest rate, which if you think logically about it, means that debt can only grow, mathematically speaking. This creates the impression that debt is always a future burden that is eternally carried forward as if it was nuclear waste.
If the market interest rate is below zero, either the government and the central bank must intervene to maintain the state of the money system above zero, because that is the only representable state. The government can subsidize the difference between the market interest rate and the money system interest rate clamp by taking on private debt and turning it private. This is particularly evident once private corporations refuse to take on further debt.
However, even if the government stopped the subsidization, you still don't get out of the conundrum. The government is patching the symptom with its cause, which stalls the problem into the future, which is "good" if the cause is considered good and only the symptom is considered bad.
The same way housing is needed for living, money is needed for trading. Similar to housing becoming an investment and therefore no longer being able to be used for its intended purpose, money can face the same fate. When people use money as an investment, it can't be used for trading. Houses sit empty and money sits idle.
It turns out that money is such an integral part of the economy that if there is no money, people can't acquire the goods they need to survive and since there is a monopoly on money systems, you can't just switch to a private provider to perform the trading you need in case the government one fails.
In other words, you either choose between a fully formalized money based economy or subsistence lifestyle with nothing in-between. The difference between the two is so stark, that a failure in the money system might as well be the collapse of all elements of society. From that perspective, it is quite smart to keep kicking the debt can down the road. Meanwhile the person who refuses to kick the can will doom society unless they implement the possibility of negative interest in their money system.
A good example of a country in a downward spiral towards UBI hell is the UK. Around 25% of the working-age population now claim to be disabled, and around 10% receive disability benefits. Labour have a genius idea for how to fix this: let disabled people try out employment for a bit to see if they like it, whilst keeping their welfare payments. So they're turning disability benefits into UBI by the back door.
The UK can't afford anything even close to this. It can't even afford the theoretically non-universal benefits schemes it has: it has massive government debt and deficits because its economy doesn't generate enough wealth, and its health welfare system (the NHS) experiences Soviet-style shortages all the time.
This has happened despite that we've been mass automating jobs with computers and robots for decades. Chips aren't magic wands that make communism suddenly work. The problems with wealth redistribution are fundamental and will never go away regardless of your level of technology.
If you disagree, fine, but please for the love of God focus on walking before you can run. Drive government deficits to zero whilst keeping growth at US levels, and then talk about more generous welfare schemes.
(you can't magic new money by eliminating means testing either, see my other comment on this thread).
I'm fairly certain its economy generates more wealth per capita than at any point in the past, and this is the general consensus. If you believe it doesn't, please explain how, as it goes against the commonly held belief.
Also, the UK's economy stopped growing in 2008.