There are plenty of plugins already that import and export variables as JSON. You can find them easily in Figma Community.

Hi! There is a plugin I came across, that allows you to filter to specific variables, export them, and it also offers an option for developers to download them in the specified format, be it css, sass or a couple of other formats. It’s called Figma Token Exporter.

Hello ​@jaclyntan, we use the Figma CSS Variable plugin in our team, which is case-sensitive and can export Figma variables in CSS. The next version will allow you to export CSS directly to GitHub or Gitlab for seamless collaboration between design and code.

Link to the plugin :
https://www.figma.com/community/plugin/1474166340745390696/figma-css-variables

I hope it meets your needs