With a CBDC, a lot of financial engineering can be done. And the CBDC will be a necessary response to the unquenchable debt. You have to think that people smarter than us know the debt growth is unsustainable and are creating some alternative system.
You are correct that the stimulus checks were much smaller than a full UBI. But, keep in mind that much of the UBI will be financed by the tech companies who are eliminating human jobs. A CBDC will allow varied taxation on every item bought or sold and every penny in wages paid. Every single transaction can incur a fee that goes toward Base UBI.
It's a gross and frightening thought, but it's something worth considering.