For plant 1000 -> the POs are flagged with GR-IV and I can't unflag the PO, the field appears in grey like freezed
For plant 1010 -> the POs are flagged with GR-IV but I can flag/unflag the PO
In standard it is not possible to control this field at Plant level but can control at document type level. Please refer the screenshot below.
Now if I use the SHD0 transaction I actually can't see any screen variant.
1) SHD0 is used for creating variant. To find out variant assignment, please use the following function.
Call transaction SE93 ---> Enter transaction ME21N ---> Check the field "Start with Variant"
2) If no variant assigned, please consult with your Technical consultant about how the status of field GR-Based Inv is controlled specific for Plant.