Due to the recent release of NS (NativeScript) 7, then Apple's release of IOS 14 and Xcode 12; there has been a lot of confusion about what works with what.
It's helpful to understand some key aspects of NativeScript in general, how they relate to what:
tns, ns or nativescript command you run to create, build, run, and debug your app.@nativescript/core (NS 7) or tns-core-modules (NS 6) - This provides a single JavaScript api to fundamental platform features for the supported runtimes, which right now are iOS and Android.@nativescript/ios (NS 7) or tns-ios (NS 6)These are all fundamental aspects to NativeScript which allows you to build a working application. In most cases, when using NS 6 CORE it requires you to use the NS 6 RUNTIME. You should normally keep CORE and RUNTIMES with the same major version.
When Apple released Xcode 12, they broke multiple build related things, including things like simulator support. So if you are experiencing an issue running against a simulator you are probably using the wrong NS CLI for the version of Xcode you are using.
Most of the TSC members have already upgraded to Xcode 12 and are using it daily to build both NS 6 & NS 7 applications. If you are afraid to update; rest assured at least for NativeScript usage, Xcode 12.0.1 is solid.
| Xcode 11 | Xcode 12 | |
|---|---|---|
| NS 6 CLI |  6.8.x |  |
| NS 7 CLI | | 7.0.10+ |
| NS 6 CORE & RUNTIME | NS 7 CORE & RUNTIME | |
|---|---|---|
| NS 6 CLI | tns-core-modules@6.5.20 | |
| tns-ios@6.5.2 | ||
| NS 7 CLI | tns-core-modules@6.5.20 | @nativescript/core@latest |
| tns-ios@6.5.3 | @nativescript/ios@latest |
| iOS 14 Supported Runtime | |
|---|---|
| NS 6 CORE | tns-ios@6.5.2 |
| NS 7 CORE | @nativescript/ios@latest |
Or if you prefer a video version, you can watch here.