You seem not to have any packages installed in your system that requires mlt6.
Perhaps it was installed as dependency of a package which no longer requires it or you have removed?
Looking at the AUR page of mlt6 it seems to be required by only two packages:
- flowblade-git (requires python-mlt)
- openshot-git (requires python-mlt)
Looking further at the dependencies of these two, mlt6 is listed for only one, namely, openshot.
Also both of these packages are outdated. They haven’t seen any updates since early 2020.
There are up-to-date versions of these packages in the official repos. None requires mlt6 and only one, flowblade, requires mlt (repo version 7.12.0-2).
Looks like you could remove mlt6.