But, people forget that CRUD apps can be as complex or simple as they need to be. A CRUD app is identified as such by its purpose, not the sophistication of it.

Right now I'm wring a web app that's basically manages some domain data in a central db, but guess the kinds of things I have had to deal with. Here a a few (there are many more), in no particular order:

- Caching and load balancing infrastructure.

- Crafting an ORM that handles caching, transactions, and, well, CRUD, but in a consistent, well-typed, and IO-provider-agnostic manner (IO providers could be: DBs like Postgres, S3-compatible object stores, Redis, Sqlite, Localstorage, Filesystems, etc. Yes, I need all those).

- Concurrent user access in manner that is performant and avoids conflicts.

- Db performance for huge datasets (so consideration of indexes, execution plans, performant queries, performant app architecture, etc, etc)

- Defining fluent types for defining the abstract API methods that form the core of the system

- Defining types to provide strong typing for routes that fulfill each abstract API method.

- Defining types to provide strongly-typed client wrappers for each abstract API method

- How to choose the best option for application- and API security (Cookies?, JWT?, API keys? Oauth?)

- Choosing the best UI framework for the requirements of the app. I actually had to write a custom react-like library for this.

- Media storage strategy (what variants of each media to generate on the server, how to generate good storage keys, etc.

- Writing tooling scripts that are sophisticated enough to help me type-check, build, text, and deploy the app just in the way I want

- Figuring out effective UI designs for CRUD pages, with sorting, filtering, paging, etc built in . This is far from simple. For just one example, naive paging is not performant, I need to use keyset pagination.

- Doing all the above with robust, maintainable, and performant code

- Writing effective specs and docs for all my decisions and design for the the above

And many many more! I've been working on this "CRUD" app for years as a greenfield project that will be the flagship product of my startup. The techniques I have to evolve to solve various challenges could easily fill entire books.