Hi @Maxime,
As it turns out, to change the icons you need to assign the array at once. Please try this approach:
fd.rendered(function () {
changeIcon(fd.container('Wizard1'), 0, 'CheckMark');
changeIcon(fd.container('Wizard1'), 2, 'Cancel');
});
function changeIcon(wizard, step, newIcon) {
const icons = wizard.icons;
icons[step] = newIcon;
wizard.icons = icons;
}
This code produces the following result:

To implement this approach, please add the changeIcon() function to your code and use changeIcon(fd.container('Wizard1'), stepIndex, 'BoxCheckmarkSolid'); instead of fd.container('Wizard1').icons[stepIndex] = 'BoxCheckmarkSolid';.