If you want to beat Real Madrid maybe not in the final but in the quarterfinals or semifinals like Man City did before. Real Madrid will be even more dangerous when they reach the final and their chances of winning are very big.
So I agree with you that, if a team wants to thwart Real Madrid's efforts in the Champions League, then they have to do it from the knockout stages including in the last 16, quarter-finals or semifinals. It's hard to expect Real Madrid's final record to be broken, but it's not impossible in the future.
I think it will take at least 1.5 decades for their record to be broken or even more. What Real Madrid managed to achieve is something legendary and that's why no other team will come close soon to actually have a chance to dethrone them.
I also don't think Real Madrid will win UCL in the next 4-5 years because even if they have Mbappe , that doesn't mean they will automatically win again. ( remember when Real had galacticos back in 2003-2008 ? and they never even reached an UCL final ? well that thing seems to repeat with this current team Real is building ).