Mobile Engineer System Design

I'm currently interviewing for a couple big companies as a mobile engineer, and they all have a round where the topic is system design. I've already had a couple and I failed spectacularly. The first

I'm currently interviewing for a couple big companies as a mobile engineer, and they all have a round where the topic is system design. I've already had a couple and I failed spectacularly. The first time was because I had never taken that type of interview before and the second was because the resources I used to learn about system design focused a lot more the server side. In fact, I still haven't found a good resource for tackling system design questions on the mobile side. Take this one for example--designing the instagram news feed. After designing the models the rest of the video goes into detail about the micro-services on the backend and handling scale. I watched similar videos about this topic and again they quickly moved onto tackling the back end. When I finally had those interviews the scope was about a single feature implemented on the front end. Let's just use an example: Building a search bar in the app. Seriously... the scope was something that small. But I have no reference as to how to go about this for a whole hour. Do I go into detail about why use mvvm? Do I go into detail about how I would implement network service classes to consume a backend api? Do I build the app from scratch and then talk about where this tiny feature will fit? (Another example would be something like a catalogue of items). When I started talking about my solution they wanted me to go into detail about the presentation layer... I thought to myself--"Seriously?" Just use a textfield to capture input and use auto-layout to fit any phone. What more is there to talk about? Do any of you have any ideas of what more I could have gone into? The latest debriefing I got for the next of these system design interviews was that they don't want me to go into the server side at all (just to reiterate how I have not found a resource that focuses on front-end system design questions). So now I'm trying to get input from anyone that has any insight. I used something like Grokking The System Design Interview (their overview of instagram) to try to get some idea as to the sort of template to use, but other than doing some requirements gathering and building data models it doesn't help much. Does anyone have a good resource on tackling this question for the mobile side--video or written doc. Every time I get this question it feels like getting hit by a bus especially since I have to talk about something so small for an hour.