Yes Butternut Squash can be put into a freezer safe sealed container and kept in the freezer for up to a year and it will still be good to eat.
Just make sure the cooked butternut squash has been sealed in a freezer safe container and it will keep just fine for up to the year although it may not taste as fresh but it's still safe to eat.
I freeze leftover butternut squash to eat later on within a few months and sometimes I forget it for a whole year and then I find it in the freezer buried at the bottom and it's still good to eat.