Minecraft Java | Order to empty inventory after death?

I wanted to ask whether there's a command for this in the Java Edition or whether it is possible with a server plugin.

What does after death mean? You lose your items anyway if you die unless keepInventory is set to true.
Explain in more detail what you want to do.

A Bedwars server for me and my friends, so when one fights against each other, the items disappear so that the other can't pick them up.

Yes, you can, you could use a plugin to remove all items lying on the floor as soon as a player dies.

So I don't know a plugin for this (but there are plugins for almost everything), but you can also automatically enchant all items with "Curse of Disappearance" by command

Shall I tell you how to do it with commands or do you really want a plugin?