OpenBSD Minecraft launchers based upon minecraft-launcher-lib
You will need the py3-minecraft-launcher-lib, jdk-11, lwjgl 3, and lwjgl ports installed to be able to use these to launch Minecraft on OpenBSD. Will work on 6.9 or later except for snapshots and the upcoming 1.17 release. Snapshots and the imminenet 1.17 release require jdk-16 which is in OpenBSD 6.9-current.
These are still pretty crude (having edit them to put in your username and password), but they work.
(Technically, you only need the lwjgl ports for 1.12.2 or earlier. Also, one only needs lwjgl3 for >= 1.13)
mc-get-cmdline.py is a script to just query the cmdline that the launcher library gets from minecraft. I use that information to generate these scripts (I need to edit them to put our OpenBSD libraries in). It might be useful for you.