If you want to have one singular button with two checkmarks, I would recommend creating a dedicated icon. This way you can also do things like making the two ticks have some minimum empty gap between each other, etc. If you insist on not wanting a new SVG asset, the least worst approach is this:
IconButton(modifier = Modifier.size(MESSAGE_CHECKMARKS_CONTAINER_SIZE), onClick = { /* doSomething() */ }) {
Box {
Icon(Icons.Filled.Check, contentDescription = "Message delivered")
Icon(Icons.Filled.Check, contentDescription = null, Modifier.padding(start = 4.dp)) // or whatever
}
}
This way it's one single button instead of two overlapping ones, which would look super weird. There can be clipping/alignment issues depending on the icons you use, and it's generally just not a great idea.