UTM error “This virtual machine cannot run on the current host machine” does not explain why

**Describe the issue**

When I start a virtual machine, UTM shows only this generic error dialog:

> **Error**
> This virtual machine cannot run on the current host machine.

The message doesn't say *what* is incompatible or how to fix it. I can't tell whether the problem is the VM image, the CPU architecture, the VM configuration, my Mac, the macOS version, or the virtualization backend — there is nothing actionable in it.

**Actual behavior**

All I get is this dialog with an OK button:


**Expected behavior**

The error dialog should explain the specific reason the VM cannot run, such as:

- unsupported CPU architecture
- virtualization vs. emulation mismatch
- unsupported macOS/host version
- missing Hypervisor.framework support
- incompatible VM configuration
- unsupported imported VM setting
- required CPU feature unavailable
- where to find relevant logs

Ideally it would include a short fix suggestion, for example: “Change the VM architecture from x86_64 to ARM64” or “Use Emulate instead of Virtualize.”

Even a “Details…” button that exposes the underlying error / log output would be a big improvement.

**Where the message comes from**

I looked at the source: the dialog text is the single `errorDescription` for the catch-all case `UTMAppleConfigurationError.platformUnsupported`:
https://github.com/utmapp/UTM/blob/fb61bfe86a2cc39bb3bc884636fa55414f317acb/Configuration/UTMAppleConfiguration.swift#L111-L112

That one case is thrown for several unrelated root causes, which is why the dialog can't say anything specific:

| Throw site | Actual root cause |
| --- | --- |
| [`UTMAppleConfigurationSystem.swift#L133-L139`](https://github.com/utmapp/UTM/blob/fb61bfe86a2cc39bb3bc884636fa55414f317acb/Configuration/UTMAppleConfigurationSystem.swift#L133-L139) | macOS guest: host older than macOS 12, **or** the saved `macPlatform` is missing, **or** `vzMacPlatform()` failed (e.g. invalid hardware model / auxiliary storage) — three different causes collapsed into one condition |
| [`UTMAppleConfigurationSystem.swift#L140-L142`](https://github.com/utmapp/UTM/blob/fb61bfe86a2cc39bb3bc884636fa55414f317acb/Configuration/UTMAppleConfigurationSystem.swift#L140-L142) | macOS guest on a non-`arm64` build (Intel hosts can't run macOS guests) |
| [`UTMAppleConfigurationBoot.swift#L65-L70`](https://github.com/utmapp/UTM/blob/fb61bfe86a2cc39bb3bc884636fa55414f317acb/Configuration/UTMAppleConfigurationBoot.swift#L65-L70) | macOS guest requires host macOS 12+ |
| [`UTMAppleConfigurationBoot.swift#L179-L182`](https://github.com/utmapp/UTM/blob/fb61bfe86a2cc39bb3bc884636fa55414f317acb/Configuration/UTMAppleConfigurationBoot.swift#L179-L182) | UEFI boot requires host macOS 13+ |

Splitting `platformUnsupported` into per-cause errors (or adding an associated reason to the case) would let the dialog state the real problem and suggest a fix.

**Configuration**

* UTM Version: the catch-all message is present on current `main` (linked above at commit `fb61bfe`); I can add my exact installed version in a comment if needed
* macOS Version: I can add it in a comment if needed — the dialog text itself is independent of it
* Mac Chip: Apple M4 Pro

**Crash log**

No crash — this report is about the content of the error dialog.

**Debug log**

The dialog appears during pre-start configuration/host validation; I can attach a log if useful.

**Upload VM**

Not specific to one VM — per the code links above, the same dialog appears for several unrelated configurations and host conditions.