1. $12k / year to everyone
2. 50% flat tax (on non-UBI income)
3. Small federal land value tax on non-wilderness properties
4. Tax on non-resident property owners
5. UBI for citizens only (to mitigate people traveling here just to not work)
But try passing that ^ in any major democracy. You can't. The reason is that the winners of the current system (most seniors, top half of wage earners, the international elite) are the ones that either vote, or set political agendas. They like being able to hire [personal helpers, maids, warehouse workers] for $12 an hour.
For a true UBI we need to raise taxes and prices a lot and that will have downsides (at least in the short term) for probably 50 to 60% of the population. We will lose workers. Real output will fall. Taxes will have to go up and we will lose some people to other job markets.
So instead people nibble around the policy edges.