I use Simple, which is similarly online-only. They recommend depositing cash by getting a money order, which you can deposit via online check deposit by taking a picture of it.
I doubt the ATMs at Target/7-11 can take cash deposits. I've only seen that feature on bank branch ATMs.
It'd be non-starter if I was, say, a landscaper and often received cash payments from clients.
I've had no trouble personally going basically cash-free. If someone gives me cash for some reason, I just buy the next grocery run with it to use it up.
I doubt the ATMs at Target/7-11 can take cash deposits. I've only seen that feature on bank branch ATMs.