This feature "Instructor speciaility" is no longer required in version 4 implementation as you design the member cards and member layouts yourself.
Also, the Instructor Only field group, is also no longer required as BuddyPress release member type specific fields in version 6.0 and WPLMS v4 is compatible with it. See below video :
https://youtu.be/AYXzAMxFWCU?t=179
These fields are simply there for backwards compatibility as many of our users are using old BuddyPress & WP as well.