This is a possible occurrence in survival, however here is a command to recreate the scenario attached in a text document because I hate the way mojang's bug reports keeps auto formatting the command.
You can summon a villager for it to attack and after the trident strikes it's target (or a block), it will return to it's rightful owner.
Unfortunately, the drowned cannot pick up the trident for... minecraft reasons; The trident thrown will instead continue to constantly hover around the eyes position of the drowned, eventually spastically spinning once it reaches a certain threshold.
I'll call this discovery, the Drowned Urchin.
Thank you for your report!
We're tracking this issue in MC-255642, so this ticket is being resolved and linked as a duplicate.
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