> specifically paying into a ubi fund whenever human jobs are replaced by ai.

Then existing firms will just go bankrupt, and new firms which never had human employees will use AI, and you’ll have the same job losses but no direct replacement and no payment into the UBI fund. Instead, just tax capital gains and retained corporate profits more than currently (taxing the former the same as normal income, with provision for both advance recognition and deferment of windfalls so that irregular capital income doesn't get unfairly taxed compared to recurring income), and fund UBI with a share of that is initially basically the difference between status quo taxes and the new rates. That realigns the incentives, such that an increased share of the economy being capture by capital (a natural consequence of goods and services being produced in a more capital intensive, less labor intensive way) drives more money into the UBI fund, without needing a specific job-level replacement count to drive the funding.