I've never had a smart phone and I don't want one. Given what we know about the 4 foundational harms to young people (addiction, social deprivation, sleep deprivation and attention fragmentation), I certainly won't be giving one to DC either. If they get to 18 and want to buy one themselves with their own money, that'll be up to them.
To answer your questions:
(i) I've never used a banking (or anything other kind of) app. I do all my banking online at a desktop computer or laptop. There's absolutely no requirement for it to be on a phone.
(ii) I've never used Google Maps or any other kind of maps on a phone. I look up where i'm going in advance and try to have a sense of the place. I have paper maps / A-Zs which I actually enjoy looking at and using. If driving, my car has a Sat Nav so I use that. Otherwise, if i'm lost, i'll ask someone. Once or twice i've called up someone on the phone and asked for directions. It's never been a problem.
(iii) WhatsApp - it's not true that WhatsApp is only available on smart phones. I use a simple version of WhatsApp on a Nokia feature phone under license from a company called HMD. It uses a very secure operating system called Kai OS X. By the way, the handset costs £50 or so and there are many far cheaper (Nokia 800 Tough) and my monthly contract for unlimited calls and texts from Vodaphone is ~£12 / month. I never use 3G/4G/5G, and only access WhatsApp where I have Wifi (home and work, usually).
I'm occasionally asked by a company / service / organisation to 'download an app', for one reason or another. If I explain that I don't have a smart phone they can always find an alternative. If there wasn't I would probably complain vociferously that they are discriminating against people who don't have a particular technology and it is their responsibility to accomodate them in another way. It hasn't happened yet..
Some might think that i'm being needlessly difficult and avoiding the requirements of the modern world out of some esoteric point of principle. Perhaps I am! I'm not against technology - I work in a technology-adjacent field and regularly use advanced scientific computing. But, I also value free space, free time to think, reading books, not doom-scrolling, not being contactable, not seeing my emails all the damn time, interacting with real life people, daydreaming, being bored, being lost (sometimes), not being a puppet of tech companies, spending quality time with my family and DC, etc etc.
Good luck