Can I mix food grade lye (sodium hydroxide) with water to make kansui?
80% potassium carbonate, 20% sodium bicarbonate at some concentration https://omnivorescookbook.com/kansui is likely to behave very differently than your sodium hydroxide.
Kansui is probably strongly buffered, while your pH is
likely to wander. That sort of thing is liable to wreck recipes.
I'd find a good how-to online, and make the stuff right.