The Eurostar buffet/bar counters used to sell paper Metro tickets, have they switched to selling the smartcard? If so it would fulfill your goal of avoiding the ticket queues at Gare Du Nord
Certainly when we travelled last Autumn, no you cannot. The card requires two (NOT passport sized) photos and filling in, so its not something you could do at the Eurostar buffet counter.
details here:
https://www.iledefrance-mobilites.fr/en/tickets-fares/media/navigo-decouverte-travel-card
If you have an Android phone with NFC hardware (most recent phones have) then you can buy and validate your ticket on your phone without the need for a smart card. From memory the Android app takes your photo a bit like the UK rail card on your phone app. However this will not work with Apple/iPhone, you can top up an existing Navigo smart card using an Apple phone, but you cannot have the ticket directly on your phone.
details here:
https://www.iledefrance-mobilites.fr/en/tickets-fares/media/smartphone
The upshot of all this is, If you have a fairly recent Android smartphone you can buy your ticket on your phone before departure, and arrive ready to go, but if you have an Apple iPhone then you have to buy the smart card on arrival and need the two photos, hence reference to queues and general mayhem at Gare du Nord.
As
@SHD stated it looks like the situation with Apple may change. I know that the French government seem to take a different view to the UK on software generally, and tend toward open source solutions, and I suspect Apple will want money from IDM hence the current situation. For local people its not an issue, they would buy the smartcard. It is only really an issue for visitors.
There is no option to use bank cards to pass through gates and pay for travel directly.
In terms of ticketing its fairly straightforwards for visitors, you buy a day, week or month pass depending on how long you are staying, and remember the 'Navigo week' is Monday to Sunday. For most visitors the weekly pass is the usally the best option at 30 euros per week.
Comparing with London there is no issues with tapping in and out, all tickets cover the purchased zones. If you use a t+ paper ticket, which I think are dissappearing then they are timed, however the down side the only way to purchase tickets is using the app/smartcard. Every so often on train or in station checks will be carried out by roving RATP staff, they scan your card/phone and check the picture looks like you
We have been using a Navigo card in Paris since 2016, and now you can top up from your phone its an easy solution, really the main issue is first time visitors with an iPhone