Assigning increase and decrease flaps to RB and LB disabled?

Do you have any add-ons in your Community folder? If yes, please remove and retest before posting.
No

Are you using Developer Mode or made changes in it?
No
Brief description of the issue:
I can’t assign increase and decrease flaps to RB and LB in the control options.
Provide Screenshot(s)/video(s) of the issue encountered:

Detail steps to reproduce the issue encountered:

PC specs for those who want to assist (if not entered in your profile)
9900K/rtx 2080 super/32GB Ram/SSD

Build Version # when you first started experiencing this issue:

1.18.13.0.

Are you on the Steam or Microsoft Store version?

Steam

Did you submit this to Zendesk? If so, what is your ticket #?
No