Is there any convention about maximum columns like 80 or 120? I just read Coding Conventions in the Kotlin website, but it says nothing about maximum columns.

I personally hold to 120, but I don't think there's an official convention for it.

The official Android coding style uses 100 (https://developer.android.com/kotlin/style-guide#line_wrapping), but Kotlin itself imposes no convention. Note that this is the style for Android’s own source code, not necessarily the recommentation for Kotlin Android code at-large, and Google usually has different style guides than what the community typically uses. I, myself, prefer 120 columns, fwiw

Use whatever lets you comfortably read two files side by side on your laptop screen

Thank you for answers!

Adam knows what's up.