This is now possible with the .slnLaunch file.

Multi-project launch profiles are available in Visual Studio 2022 17.11 and later. To enable or disable the Multi-project Launch Profiles feature, go to Tools > Options > Preview Features and toggle the checkbox for Enable Multi Launch Profiles.

See: https://learn.microsoft.com/en-us/visualstudio/ide/how-to-set-multiple-startup-projects?view=vs-2022