It’s not that simple.
Neither is it a simple religious difference. It is religion merged with ethnic differences.
Kosovo was probably “Albanian” tribes during the Roman and pre-Roman period (until the 6th century). It was then Slavic owned (and probably slowly Slavicized) from the 6th century to the 14th century.
It was part of the state of Serbia for centuries before the 14th century.
It’s demographics changed - both ethnically and religiously from the 14th century.
After the re-establishment of the Serbian state in the 1800s it was still demographically majority Albanian and majority Muslim (including Muslim Serbs) even as part of the Serbian and then the Yugoslavian state.
I would note that in Albania proper you have Mulims, Orthodox Christians, Catholic Christians living peacefully together. And in Bulgaria you have Orthodox Christians and Muslim Bulgarians (Pomaks) living together.
It could have worked in Kosovo if
1. The “ethnicity” or the “religion” was the same — I’ll note that most Kosovar Muslims are Sufi,
2. The Serbs were not trying ethnic cleansing - if they had just instead using “ethnic pressure”, then the population would have changed gradually.
What can be done now?
I think the blood is too bad after killings on both sides to have a unitary state.
Splitting it in two would be the “logical” option, but won’t work as many Serbian historically significant places are in Albanian hands.
Ethnically cleansing it one way or the other is also impossible even if one could stomach the morality of it.
Perhaps a solution wherein Kosovo is a “Sud-Tirol” state would work?
A perfect explanation of European stupidity that will always keep them a petty and unaccomplished people. They all have gripes and complaints from 1500 years ago. And they all boil down to “they are different”.
America was the place that left that behind. A curse on those who try to drag America into those idiotic meaningless old world feuds.