Navies are known to use low frequency radio to send messages to submerged subs.

This uses the same principle, but the traditional method required immense antennas and very high power radio transmitters.

Such antennas and transmitters cannot be installed in a small submarine.

Here a new kind of antenna is used, which is efficient under water even at small dimensions, so it can be installed in small submarines, for communication at distances of up to a few hundred meter.

But isn't torpedo steering still dependent on wire?

The issue is it doesn't really matter and radio isn't much benefit: you get much higher bandwidth, better reliability, immunity to ECM, and fiber-optic wires in Ukraine are over 50km long.

The exact application for this is autonomous underwater vehicles where what you would like to do is communicate quickly and without a tether in arbitrary scenarios - i.e. think a bunch of autonomous vehicles which might need to relay a message or communicate with dropped assets. Using radio in those scenarios solves the problem of a consumable (the wire), and also the problems associated with sonar like fouling of the array.

fair enough but afaik torpedoes aren't tethered by a fiber optic cable like drones. it's a much thicker cable that possibly contains a fiber optic cable.