How is this any different from native code? Afaik, you can access the native compiled source code of an app on a jailbroken phone. Sure it's more of a pain to parse through but security through obscurity isn't security.
Definitely, running "strings" on a binary is about as easy as finding the JS for a hybrid app (WebViews or React Native). Depending on your experience it could be easier to extract API keys from an IPA than from JS.
In either case the root issue is about sending secrets like an unscoped API key to the client. "Client secret" is an oxymoron in this context regardless of the programming language.
You'd have to know a few things first, like (1) the IPA is a ZIP file, (2) the ZIP file is actually of a directory and (3) you can dump the actual code in the JS files (if they're in the bundle directory) much easier than you can look for strings from the binary that might look like an API key.
The API key is actually the least of the hazards, since you can hide that in the keychain. Having source code for your business logic shipping in your app is not good; having it be hackable business logic (by changing the JS in place) is very not good.
Shipping source code with business logic (assuming the definition of source code includes obfuscated JS) is how the entire web works today! With WASM the code that is shipped will be even further away from the original source code and really not so different from downloading ARM from the App Store or Java/ART bytecode from the Play Store.
Not the entire web. eBay and Amazon don't put all their algorithms in the browser; PayPal doesn't either. They hide their company jewels behind their API where they're a little more secure. What you see in the browser is the presentation layer code.
Hybrid apps could achieve that same kind of relative business logic security, but at the cost of pushing more and more of the actual business logic behind an API and not in the JS in the app. At that point, the benefits of code sharing (such as they are) get fewer and fewer since it's really pretty easy to write API code in Objective C, Swift, Java or Kotlin.
You aren't "parsing" through compiled (and linked) code; you're decompiling it, which is a much trickier thing to do and get right. Having your app logic in Javascript in the sandbox cache is just serving it up on a plate.
In either case the root issue is about sending secrets like an unscoped API key to the client. "Client secret" is an oxymoron in this context regardless of the programming language.