The spawn rates are the same in both Minecraft Bedrock and Java Edition. String is an integral item in the crafting recipe for bows, fishing rods, bundles (whenever they get added in future ...

A Drowned has a 3% chance in Minecraft Java Edition and an 8% chance in the Bedrock Edition of spawning with a Nautilus Shell in its hand. If it does, this will be dropped once it’s died.

You can easily get dozens of Sticks with just a few Planks and you'll need them for plenty of other basic recipes in Minecraft. As for String, that's a bit tougher to come by.