Copy (Command-C) stopped working in Preview

Unable to copy formatted text while in Preview mode. Experiencing issue in 1.11.1.

### Expected
Create new document. Enable markdown formatting. Add some basic text such as:
```
This is a test
# Test header
- Test bullet
```
Click on Preview. Select some text. Unable to copy the Preview formatted text.

### Observed
The Edit / Copy menu is greyed out.

### Reproduced
My apologies, see Expected section above.

Simplenote: 1.11.1
MacOS 10.15.5
MacBook Air 2018 (but I doubt this is hardware-specific)

Reproduce the issue in the macOS Preview mode using a document containing plain text, a heading, and a bullet list, as described in the report. First inspect how Preview handles text selection and the Edit/Copy menu state; done means formatted Preview text can be selected, copied with Command-C, and pasted elsewhere.

Written by the indexing model from the issue text.