A Dripleaf is one of the many new items that were added in the recent update for Minecraft, and to get it you must locate a lush cave. To find lush caves, you will need to first locate a specific type of tree called an Azalea tree.
However before going off to look for these trees, please note that both lush caves and dripleafs are not in the main branch of the game yet. Both should arrive later this year in update 1.18, and when that happens, this method will work, but it will not work for branch 1.17.
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That said, you need to find Azalea trees because they will always spawn above a lush cave, so if you dig down near this tree, you are sure to locate the lush cave. You can also best identify one by their pink flowers in the leaves pictured below.
Once you locate the cave, you will need to then go for a bit of exploring, and eventually, you might run into a leaf that looks like the one below.
This is the Dripleaf, and it will grow in places like the one above inside lush caves, and if you want this leaf, you will need to mine it with an axe. Once you got the leaf, you can then use as a platforming or parkour block or for some nice decoration for your base.