Is there a way to implicity pass some data to parent composable without hoisting the state? I basically need to let the parent know if it contains a specific kind of optional child composable.

Check

Modifier.layoutId()

and

ParentDataModifier

.

That's not something I can use, unfortunately as I'm working in compose-web context. I need something more generic.

Then you should ask in #compose-web as it's (almost) a completely different thing.

It's not a web specific issue though. I just need a solution that only uses compose runtime and not android/desktop specific constructs

I don't think there's such a way. Compose runtime has no knowledge of actual parent/child nodes and apparently compose desktop/Android and compose web use different node types.

I wonder if there’s anything like

SubcomposeLayout

for web?

Why don't you want to hoist your state?