Bilbao does look quite consistent this season. Be it in Laliga or in the European League. The last time this team experienced defeat was in the match at the beginning of October when they lost to Girona with a score of 2-1 at Girona's home ground. And that happened as a result of the red card received by Bilbao and Girona scored a goal in the added minute of time through a penalty kick opportunity. So in that match Bilbao actually lost, not because they were weak, but because they were just unlucky because they had to lose one player due to a red card in the final minutes.
And if you later today will favorite Bilbao then I will understand the reasons you have. It's just that I personally will probably still favor Real Madrid. Even though Vinicius Jr and several other important players in the back line are still not back, I see Real Madrid starting to adapt to their own situation. And Mbappe also seems to have started to find his rhythm again and can adapt to Real Madrid's attack line. Therefore, I will still favor Real Madrid and maybe Real Madrid will win even with a narrow score.
In my opinion, if I have to choose one, Madrid still deserves to be the favorite.