Android 6.0 introduced a new feature called Direct Share that allows apps to pin a more specific set of targets to Android's share menu. You've probably seen it already—messaging apps will allow you to share a file directly to a specific contact instead of just to the main app, and there are several other implementations like this.
But even though Direct Share is quite useful in theory, many apps will not allow you to disable the feature. This results in a cluttered share menu that's filled to the brim with both Direct Share targets and traditional entries, which can take up most of your screen at times, rendering the share menu almost useless.
Luckily, though, a popular Xposed module lets us selectively disable Direct Share targets. The setup is pretty simply, and it goes a long way towards reclaiming Android's share menu, so I'll show you how it works below.
To get started, head to the Download section in your Xposed Installer app, and search CustomShare, then tap the top result. From here, swipe over to the Versions tab, then hit the "Download" button next to the most recent entry. Within a few seconds, Android's installer interface should come up, so tap "Install" on this screen.
Then, once you've got the module installed, be sure to activate and reboot to wrap things up.
When you get back up, go ahead and open the CustomShare app, which you'll find in your app drawer. From here, you'll see a list of all the apps that have either traditional share intents, or Marshmallow's new Direct Share feature.
To remove an app from your share menu in its entirety, simply tap it in the list, at which point the entry will turn red. But to remove the Direct Share targets specifically, long-press the app, at which point the entry will turn pink to signify that the Direct Share functionality in this app has been disabled.
You can repeat this same process for up to 9 different apps, which should be plenty for most folks. But if you'd like to hide more share menu entries than that, you'll have to purchase the CustomShare Donator app for $2.66.
Once you've removed any unwanted Direct Share entries, your share menu should be a lot easier to use. Without all of the excess, Direct Share is actually a really nice feature, so reclaiming your share menu should go a long way towards making the feature more useful.