I can't drag and drop files in finder after Mojave 10.14.6 update!!

Does this occur for a different user, e.g., Guest? How to test an issue in another user account on your Mac.

Does this occur after starting up in Safe Mode?

Consider the possibility of a third party software conflict.  EtreCheck can be used to investigate what is installed.

vanefiore wrote:

I just updated my OS to Mojave 10.14.6 and I can no longer drag and drop files in Finder. I'm guessing this is a bug?

Update from what to what? macOS 10.14.6 has been out for quite some time—

Rebooting is always the first step.

You can try re-applying the combo update to sort one off anomalies like yours—

Combo update 10.14.6 https://support.apple.com/kb/DL2010?viewlocale=en_US&locale=en_US

More like a glitch.

Try restarting, then maybe reinstall the OS.