The transition away from Lua for luci applications started back with 21.02.
https://openwrt.github.io/luci/jsapi/LuCI.uci.html
You'll probably want to convert to javascript, not ucode. Like @slh pointed out, many luci applications have been converted to javascript already, you'll be better off browsing the source code and/or reviewing documentation: https://openwrt.github.io/luci/jsapi/