How to create custom rememberState in jetpack compose?

Yes, you can create rememberable functions such as rememberModalBottomSheetState or rememberLazyListState. Creating custom remember functions that store multiple data type or MutableStates are common. Putting Composables is not common, at least i haven't seen so far, but it's doable.

class MyState internal constructor() {
   var state1 by mutableStateOf(0)
   var state2 by mutableStateOf(0)
   var someValue = 0
}

internal constructor is optional, it's for restricting developer to create instance only by remember function.

// you can add params to pass to MyState instance or keys to reset remember
@Composable
fun rememberMyState(key1: Any?): MyState {
    return remember(key1) {
        MyState()
    }
}

If you wish to add Composables one way of doing it is

class MyState internal constructor() {
    var state1 by mutableStateOf(0)
    var state2 by mutableStateOf(0)
    var someValue = 0
    // this can also be SnapshoStateList to trigger recomposition when you add, remove or update list with new item instance
    val list = mutableListOf<@Composable () -> Unit>()
}

Usage

val myState = rememberMyState(key1 = Unit)
myState.list.add {
    Box(
        modifier = Modifier
            .fillMaxWidth()
            .height(100.dp)
            .background(Color.Red)
    )
}

myState.list.add {
    Box(
        modifier = Modifier
            .fillMaxWidth()
            .height(100.dp)
            .background(Color.Yellow)
    )
}

Column(modifier = Modifier.fillMaxSize()) {
    myState.list.forEach{
        it.invoke()
    }
}