There already exist plants adapted for optimal yields at lower CO2 levels. They are classified as C4 plants and hit optimal photosynthesis at about modern levels. These include corn and sugarcane, but only make up a small fraction of overall plant species (about 5%).

C3 plants hit optimal levels at higher concentrations, usually 1100-1300 ppm (90% of plants fit this category). See link below for more details:

https://rclutz.wordpress.com/2020/01/08/heres-looking-at-you...

Now I don't know how the mechanics work. I don't know if you could genetically engineer a C3 plant to work as well as a C4 plant. I reckon there are significant tradeoffs there that nature already factored for.