Hi Orby,
That is probably something to do with how the file is set up.
If it’s an old version, it was probably set up for proxies. Which means the actual rig was hidden in the original file. But for Overrides, it should be visible (otherwise it’s invisible when it’s linked in). Oh and don’t forget there are 2 ways of hiding – with the eyeball and with the computer screen icon. Both of them will need to be enabled.
You could also try to reorganise the collections.
I usually have a master collection which has ALL the component collections in it (I name this will ALL CAPS)
And then I put the geo and rig in its own collection. (I also have the actual rig in 2 places, the master collection and the ‘rig’ collection)
This is just so it’s easier to find when you are animating but still has it’s own collection.

I hope that image helps. I don’t have the crane arm project synced on my computer at the moment so I can’t show you how to do it for YOUR rig.