You are right. I forgot about Atletico Madrid who also beat Real Madrid this season. And yes, this can indeed provide a big picture that Atletico Madrid cannot be underestimated. But I remain confident in the performance of Inter Milan, who are still the best team in Serie A this season. And as you said, Inter Milan has strong drive and motivation to reach the top of the UCL final again. But yeah, Inter Milan won't have an easy match. So losing or winning probably won't be a surprise for the Inter vs Atletico Madrid match.
In 2023 - 2024, Atletico Madrid ever defeated Real Madrid 2 times. Meanwhile Real Madrid defeated Atletico Madrid 4 times. It is very clear that Real Madrid is still superior against Atletico Madrid. But of course no team must underestimate Atletico Madrid because they can surprise us. They even could defeated Real Madrid in crucial matches. However, Atletico Madrid will play against Inter Milan in UCL, it is very different when they play against Real Madrid. In my opinion, Inter Milan has a better defense than Real Madrid and their main striker (Lautaro Martínez) looks in their best form this season. Another reason, Inter Milan played very impressive in Serie A, they also could reached the UCL final in the last season. With these matters, it seems quite difficult for Atletico Madrid to win against Inter Milan. But we can't deny that it is not impossible for a surprising result because UCL matches often surprised us in each season. 
Please take a look: https://www.soccerstats247.com/h2h/atletico-madrid-real-madrid-15692-16110/