[Q] Why I can't see my system partition after installing a rom without mounting it?

Hello.
My problem is that i installed BrokenOS on the Alcatel One Touch Pixi 3 (4) without mounting the system partition in TWRP.
When i connect the phone's storage to my pc i only see Custpack, Cache, Internal Storage, and MicroSD Card.
Without the system partition i can't even install gapps.
What should I do?

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