GoogleMap workaround to keep bearing:

GoogleMaps+Extensions.kt

/**
 * map.animateCamera(CameraUpdateFactory.newLatLngBounds()) will lose ignore current bearing and rotate the camera
 */
fun GoogleMap.animateToBounds(bounds: LatLngBounds, width: Int, height: Int) = animateCamera(boundsToCameraUpdate(bounds, width, height))

/**
 * map.moveCamera(CameraUpdateFactory.newLatLngBounds()) will lose ignore current bearing and rotate the camera
 */
fun GoogleMap.moveCameraToBounds(bounds: LatLngBounds, width: Int, height: Int) = moveCamera(boundsToCameraUpdate(bounds, width, height))

fun GoogleMap.boundsToCameraUpdate(bounds: LatLngBounds, width: Int, height: Int): CameraUpdate {
    val zoom = getBoundsZoomLevel(cameraPosition.zoom, bounds, width, height, GeneralMapStrategy.MAX_ZOOM)
    return CameraUpdateFactory.newCameraPosition(
        CameraPosition.Builder()
            .target(bounds.center)
            .zoom(if (zoom >= GeneralMapStrategy.MIN_ZOOM) zoom else cameraPosition.zoom)
            .bearing(cameraPosition.bearing)
            .tilt(cameraPosition.tilt)
            .build()
    )
}

/**
 * north west ----------- north east
 *  |                         |
 *  |                         |
 *  |                         |
 * south west ---------- south east
 *
 * note: only tested for north west hemisphere
 */
fun GoogleMap.getBoundsZoomLevel(currentZoom: Float, bounds: LatLngBounds, mapWidthPx: Int, mapHeightPx: Int, maxZoom: Float, padding: Float? = null): Float {
    val nePoint = projection.toScreenLocation(bounds.northeast)
    val swPoint = projection.toScreenLocation(bounds.southwest)
    val width = (swPoint.x - nePoint.x) + (padding ?: 128f.px)
    val height = (swPoint.y - nePoint.y) + (padding ?: 128f.px)
    val latZoom = currentZoom + log2(mapWidthPx / width)
    val lngZoom = currentZoom + log2(mapHeightPx / height)
    val result = min(latZoom, lngZoom)
    return min(result, maxZoom)
}

About the padding, no real reason except it looked a bit nicer for my use cases. Regarding zoom I needed 16 to 19 but I suggest playing around with it. You don't have to constraint the user if there is no requirement. Kinda also depends on the map viewport size.