Start here, because it is the mistake that strands people. Kosovo is outside the EU and the EEA, so Roam Like At Home does not apply. Your EU plan's home allowance does not cover Kosovo, and using it there is charged as international roaming.
Kosovo is inside the Western Balkans Regional Roaming Agreement, which is a separate arrangement between the six Western Balkans partners. If your SIM is from one of those, that is worth checking. It is not the EU regulation and it does not help a visitor from Germany, France or Italy.
The second trap follows from the first: Kosovo is frequently left out of Europe regional eSIM bundles. Travellers report buying a Europe plan, arriving in Pristina, and having nothing. Read the country list on any regional plan rather than assuming Europe means all of Europe.
So for almost every visitor, Kosovo needs either a Kosovo plan, a regional plan that names Kosovo explicitly, or a local SIM.