<font-awesome-icon icon="fa-duotone fa-angle-up" />
<FontAwesomeIcon icon="fa-duotone fa-angle-up" />
.my-icon {
position: relative;
font: var(--fa-font-duotone);
font-style: normal;
}
.my-icon:before {
position: absolute;
content: "\f106";
opacity:0.5
}
.my-icon:after {
content: "\f106\f106";
}
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 384 512" style="width: 30px;height: 30px;fill: black">
<path d="M352 352c-8.188 0-16.38-3.125-22.62-9.375L192 205.3l-137.4 137.4c-12.5 12.5-32.75 12.5-45.25 0s-12.5-32.75 0-45.25l160-160c12.5-12.5 32.75-12.5 45.25 0l160 160c12.5 12.5 12.5 32.75 0 45.25C368.4 348.9 360.2 352 352 352z"/>
<path style="opacity: 0.5" d=""/>
</svg>
<i class="fa-duotone fa-angle-up"></i>