We emit about 40 billion tons a year, so that would imply we need the entire world's electricity supply to capture 40 thousand tons.

This single tiny test plant is capturing 4 thousand tons.

The number you read is wrong by miles.

If we look at $100 a ton and guess that half of that is power at 10 cents a kWh, we would need 20 petawatt hours per year. Current world production is 25 petawatt hours per year.

The prototype uses the excess capacity of existing industrial infrastructures which is many, many orders of magnitude smaller than is required to meaningfully reduce atmospheric CO2. It uses chemicals that are extremely energy intensive to produce from mined minerals. Scaling the raw inputs would require massive scaling mining, energy production, logistics, etc far beyond anything that has ever been done before by a very large margin.

Their $100 per ton is extremely optimistic because it doesn't require building the upstream supply chain that can feed their processes at the required scale. It isn't like this is something that already exists, it all has to be built from scratch, is amortized into the cost per ton, and has much worse than linear scalability. I'm not sure how to accurately convey just how qualitatively inaccurate your perception of our capacity to do this at scale is.

Constructively, I'd like to see the argument that we can manufacture the potassium hydroxide at the scale required to sequester all 20th century CO2 in 20 years. The math, inputs, and capacity for the entire supply chain are public. There is much opportunity for rigor but even cursory analysis shows that it is not remotely feasible to effect CO2 sequestration this way even with heroic efforts. And that is under the most ideal of circumstances.