Do Europe committees care about my community service for GRE learners?
Q: So, is it worth the space to mention about the contribution for GRE learners?


I see no difference in this matter between US and European schools. If you felt it was worth the space for the US, keep it in. Your "community service" was to create a Anki deck for a common test. Whether the school you are applying to is using this specific test or not does not change the value of your contribution.

If you are worried that the admission committee reading your application does not know the GRE, you can always add a short sidenote that explains what it is.