Introduction of French native speaker lerning German and Russian


I am a French native speaker, I speak English fluently.
I am trying to bring my German from intermediate to Fluent.
I am learning Russian with various app and I am aiming to reach basic proficiency.
I am using DuoLingo, Babbel and Busuu.
My experience with various apps is that is good to start and assimilate basic knowledge but I am looking for an app to boost my mastery of German grammar and vocabulary which I will need to pass B2 and C1 exams.
I am mainly studying languages during my commute to work, hence my preference for apps. I am working by 10-15 minutes sessions maximum. I completed to German courses on Busuu and will try various solutions to bring my German to the next level.
I also like to learn new languages but I have not declded which one will be the one I choose for good.