I have designed an umbrella holder for the trunk.
Two hooks are needed that hook into the Isofix holder in the trunk.
I have printed them in TPU but it should work in any other material.
I think it should work for any car with Isofix points in the trunk.
Here is a version with two hooks:
Umbrella mount Isofix double hook Remixed by Magr099 - MakerWorld