IMPORTANT

Please verify first that having one process for per instance will allow the implementation of copy/pasting audio data across projects like AU3 can.
Slack conversations on the topic (internal):

• https://mu--se.slack.com/archives/C06RX437GJV/p1728554588586659?thread_ts=1728485687.916899&cid=C06RX437GJV
• https://mu--se.slack.com/archives/C06RX437GJV/p1728558320061249

Bug description

• AU4 cannot open projects via 'File -> Open...' if a Project already has been opened.
• AU4 cannot create a new project if the User has opened a project already.

If no current project is opened, everything works as it should.

Steps to reproduce

1. Open or create a new project
2. Go to 'File -> New'
3. Observe Result
4. Go to 'File -> Open'
5. Open another project
6. Observe result

Expected behavior

User should be able to open projects when a project is opened already.

Actual behavior

User is not able to open projects when a project is opened already.

Audacity Version

f4c0557

Operating system

Windows, Linux

Additional context