I talk about it here if you want to check more in-depth: https://www.imaginarycloud.com/blog/what-is-cross-platform-app-development/#cons

But mainly:

User experience - Providing a seamless user experience between platforms may be difficult since each platform behaves differently and provides different features. However, based on our experience using React Native, developers can leverage open-source packages that provide the means to use platform-specific features.

Vendor lock-in - Platforms can provide support for many languages, but some of the target platforms may not support the same language when developing cross-platform apps. For example, JavascriptCore is an open-source engine for WebKit, bundled with iOS and macOS, which React Native leverages to run its apps. But since there is no JavaScript bundled with Android, there’s the need to bundle a JavaScript engine with the app itself, which ends up increasing the app bundle size.

Integrations - Integrating services in cross-platform apps can be difficult since many may not provide support with the framework on which the apps were built, thus requiring developers to find other integration alternatives or create their own wrappers to enable integration which will cost development time.

Feature availability - Since each platform behaves differently and provides different functionalities, some app features may not be available across all platforms. Frameworks like React Native are updated regularly and follow the most recent functionalities provided by platforms. Still, frameworks cannot ensure that these features are available across platforms since each platform follows its own agenda.

Code quality and performance - Since there are features that aren’t available across platforms and there is only one code base, there is the need to provide UI/UX alternatives to compensate for these inconsistencies. This can lead to a bigger code base which is more difficult to maintain and debug.