WRITTEN BY RIYA DUBEY
Vegito is the fusion between Goku and Vegeta. It is a fusion using Potara earrings and is a bit different from Gogeta. It is also the strongest fusion in the entire series of 'Dragon Ball'.
Beerus is one of the gods of destruction and is a god of destruction for universe 7. It is hinted that he is quite possibly the strongest god of destruction among the current 12.
It is unlikely that the two will fight, considering Beerus is training Vegeta and is a little fond of Goku. But in a hypothetical fight between the two, Beerus will ultimately win.
Vegito is exceptionally strong and the SSJB evolved is very strong and it helped Goku and Vegeta to almost defeat fused Zamasu. However, this is still not enough to defeat Beerus.
Beerus has the upper hand in battle due to his experience and his status as a god of destruction. Because he is a god of destruction, he can use Hakai which can destroy things and people and if directed at Vegito, can ultimately destroy him.
However, Vegeta himself is learning this technique and hasn't mastered it, which means Vegito would be unable to use it as well.
In addition to that, SSJB evolved form was unable to defeat Jiren, and Beerus is stronger than Jiren. This is another reason why Vegito in this form, will be unable to defeat Beerus.
That is not to say that Vegito will never be able to surpass Beerus. This is the strongest fusion in the series and as both Goku and Vegeta grow and unlock more forms, they are very likely to surpass Beerus one day in their fused form.