To be honest there's nothing special in the code or whatever.
Almost all the apps I worked on are at least 50MB so it does not surprise me.
The smallest one I've worked on is a 2 screens app, 100% offline, without any third-library, without in-app purchases and without onboarding etc so it's clearly the less you can do and it's still almost 20MB.
iOS apps are big. I checked my top 10 results for “budgeting” in the store and this app is smaller than half of those.
It does strike me as odd that apps are so big these days, but this one isn’t particularly large.