I downloaded Minecraft blocks and append one of the objects to another blender file. but I can't move this yellow box which I appended from the file (I tried to move this with G from the keyboard as usual). so I opened the right item section for moving the objects by using that sidebar. however that transform section is not active so that I still can't move the box..is there anyone who knows how to solve this problem..!?
Looking at the chain link icon beside the object name, you didn't Append the object but Linked it.
You can't move linked objects directly, you have to use a proxy (old way) or a library override (new way).
If you want to retain the link to the original file, right click on the object in the outliner, then go to ID Data > Add Library Override.
If you want to have the object act independently of the original file, like it would if it had been appended, you need to right click on the object in the outliner, then go to ID Data > Make Local.
Another option would be to put the object in a collection and make only the collection an asset. When linking the collection from the Asset Browser into the 3D Viewport it will then be transformable. You will however need to put the object in the original Blender file at location (0,0,0), otherwise the object's Gizmo will be skewed to location (0,0,0).