Is there any uniform approach for scanning QR-codes on multiplatform? I need iOS/Android/Desktop JVM

Maybe this one https://github.com/alexzhirkevich/qrose

Scanning, not generating

You might could use ZXing for Android and JVM

There's none yet. Google has a QR code scanning library, which is substantially better and faster than ZXing, and now works without having to develop the Camera UI

I'm going to be annoying... generate them on a server?

This is the best I can find: https://youtrack.jetbrains.com/issue/KT-61832/Kotlin-Multiplatform-native-iOS-functions-not-working-as-expected