Well, I've never cooked my freezer jams so the plums wouldn't be turning to mush in my case.
You can work them through strainers and gradually get smaller and smaller bits. It can be hard work but with plums that are ripe you don't have to worry about them being too much of a struggle.
The thing "I" like about freezer jam is that you open it up, scoop some out, and put the container back in the freezer to stay frozen until you need more. I currently have 6 tubs of strawberry freezer jam and 4 of raspberry freezer jam in the deep freeze. I have 1 tub of each in my fridge freezer.
Freezer jam isn't like other jams and jellies. It's better since there aren't any preservatives or additional gunk except fruit and some sugar and pectin to thicken it.
That's why I make it like I do. There are many different recipes for non cook freezer jam. You can google them.