You might get more help in the CircuitStudio forum, since that’s more closely related, but not sure how active it is.
What is the Outline layer used for (see attached picture)?
It should be used for the actual outline of the board. Some people use the ‘keepout’ layer in Altium, and sometimes the .gko file extension for the corresponding gerber, but that’s logically a different thing with a different purpose. The outline layer should include all of the edges of the board, including internal edges around holes. Some fabricators request you mark internal cutouts specifically, ie “CUTOUT” text inside of the cut outlines, but I think generally they’ll assume that’s what you want. But if they see tracks/pads/vias inside of those outlines they’ll flag it, since they assume you probably didn’t mean to route through those features.
I know that the "Drill drawing" layer is how you ask for holes to be cut into your project.
Sort of. As above, holes *routed* into the board should be in an outline layer. The drill drawing layer is for documenting *drilled* holes, but since all of the necessary fabrication data for drilling is generally present in the NC drill files, it’s not often used. It might be useful if you’re doing boards with blind/buried vias or some other very particular fabrication requirements, but I don’t make those sorts of boards and have never used it.*
In the PCB component properties, is there an ‘unlock primitives’ option? Or maybe in a context menu? In Altium, that would let you select the primitives in the footprint and delete them without having to go in to the library and edit them there.
Alternatively, you could use a different layer for your board outline and generate your outline gerber from that. There’s no real difference between the gbl, gtl, gbo, etc gerber files in terms of formats, it’s just a naming convention. So as long as you can get a gerber with the right data out of the software you can freely rename it as needed before sending to the fabricator.
*OT, but I actually have a hard time imagining a scenario where a drill drawing is useful given modern boards and fabrication methods. CAM tools don’t need a visual representation of what size holes to put where, just a list of coordinates and sizes is fine. Same for inspection tools, or for planning blind/buried stackups. It’s not like humans are doing the drilling, or even closely supervising the drilling, these days! Maybe if you want a visualization of how different drilling operations/hole types are distributed over a board for DFM or process optimization purposes, but I expect CAM tools can do that better from the machine-readable listings as well, with interactive filters and so on. But I don’t know — maybe I overestimate the capabilities of modern CAM tools