Hey Kamoi
Sending text to a lightbox is done by adding it as an object to the call
Some basic code:
//Site Code
let dataObj = {
"text1": "Some Text",
"text2": variable
}
wixWindow.openLightbox("LightboxName", dataObj);
On the lightbox you would then read that with getContext()
import wixWindow from 'wix-window';
$w.onReady(function () {
let context = wixWindow.lightbox.getContext();
$w('Element').text = context.text1
$w('Element').text = context.text2
})