Enable Variant 'SAVE' button while using 'REUSE_ALV_GRID_DISPLAY'

The SAVE button is not active by default in GRID status, you should create an own status.

But if you mean the button to save a layout variant, you have to set the parameter I_SAVE:

SPACE = Display variants cannot be saved
Defined display variants (such as delivered display variants) can be selected for presentation regardless of this indicator. However, changes cannot be saved.

'X' = Standard save mode
Display variants can be saved as standard display variants.
Saving display variants as user-specific is not possible.

'U' = User-specific save mode
Display variants can only be saved as user-specific.

'A' = Standard and user-specific save mode


<<참조>>

  call function'REUSE_ALV_GRID_DISPLAY_LVC'
    exporting
      i_callback_program       = sy-cprog
      i_callback_user_command  = 'USER_COMMAND'
      i_save                   = 'A'
      it_fieldcat_lvc          = gt_fcat_lvc
      is_layout_lvc            = gs_layout
      it_events                = gt_events[]
    tables
      t_outtab                 = gt_itab .