I just ordered some boards via the Fusion page, and I was puzzled that nowhere in the page (where you say what kind of board you want, how many etc) was there a question “Do you want your order panelized?” What I’ve ordered is the standard 100mm square, but I want it cut into 4 sections each 25x100mm, all with the same design. I’ve sent Gerber files showing this, with the separation lines shown on the Outline layer as the instructions say, so I hope that causes the panelization to be done. I would have expected the system to ask explicitly about panelization, though. But then I thought, even if they don’t separate the boards for me, I can do it myself and although the manufacturer would cut the boards more neatly, I still want to place the order, so that’s what I did. Either I’ll get 10 big boards, or 40 little ones.
You pretty much get what your Gerber board outline (GKO) says. If you want individual boards, then just send a single board design and they will deliver individual pieces. Clearly they are panelizing your design for the convenience of manufacturing anyways behind the scenes. If you want to receive a panel with multiple boards still intact, then design your panel and put Vcut lines on the board outline to indicate where you want it scored or use routing and mouse nibbles to partially separate the individual boards.