im on kubuntu and minecraft before 1.13 crashes

Minecraft versions before 1.13 require Java 8 to run. You need to install Java 8 manually on Linux.

For more help, please use the community support discord server, linked below.

Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – ✍️ Feedback and Suggestions – 📖 Game Wiki