Italian plums are prune plums, but when you dry them at home they have none of the soggy gumminess of store-bought prunes, and much more tang and flavor.
If you have a dehydrator or slow cooker/air fryer with a dehydrating setting, these plums will be easy to dry. But a very low oven (140 or less) will also work. Simply halve or quarter the plums, lay them on cooling racks set on baking sheets, and let them bake for 10 - 18 hours. You can choose to do this over several days - putting them into a cooling oven after baking or roasting something else - or over the course of a day and a night. You want all moisture to be removed from the fruit.
Once the plums are completely dried and cooled, store them in a jar with plenty of room. Shake the jar every day to make sure there is no residual moisture left in the fruit (which could create mold). If after a week no moisture or stickiness has appeard in your jar, you can be sure the fruit is safe to store longterm.