Here in the /e/ forum you can find several reports on this topic.
The most important thing before buying is to know that Samsung distributes two different versions of the Samsung Galaxy S9+ - “star2lte” worldwide.
For /e/OS ROM you need one of Europe/Global (EMEA) model: SM-G965F, SM-G965F/DS, SM-G965N with chipset Samsung Exynos 9810. Other models are not supported
For example, here you can track a recently successfully completed /e/ OS ROM installation.