Building different Solution Configuration in Appveyor for each platform - appveyor

Question

I am attempting to add Linux building and testing to a C# library I maintain. One library in the solution requires WinForms and so cannot be build on Linux. I added a ReleaseNoGui configuration to my solution, and I would like Linux to build that rather than Release. Is this possible? This is what I've tried, but it is still building Release.
(…)
image:
- Visual Studio 2019
- Ubuntu1804
configuration: Release
(…)
build:
project: MySolution.sln
parallel: true
verbosity: minimal
publish_nuget: true
publish_nuget_symbols: false
for:
-
matrix:
only:
- image: Visual Studio 2019
deploy:
- provider: NuGet
name: nuget_release
api_key:
(snipped...)
-
matrix:
only:
- image: Ubuntu1804
configuration: ReleaseNoGui

Answer 1

for.matrix specializes configs based on environment variables. Currently, image is unsupported environment variable.
To achieve what you want you can use the following appveyor.yml config instead:
environment:
matrix:
# Windows job
- job_name: Windows build
appveyor_build_worker_image: Visual Studio 2019
# Linux job
- job_name: Linux build
appveyor_build_worker_image: Ubuntu1804
matrix:
fast_finish: true
configuration: Release
build:
project: MySolution.sln
parallel: true
verbosity: minimal
publish_nuget: true
publish_nuget_symbols: false
for:
-
matrix:
only:
- job_name: Windows build
deploy:
- provider: NuGet
name: nuget
-
matrix:
only:
- job_name: Linux build
configuration: ReleaseNoGui

Answer 2

After reading Feodor's answer, I experimented with environment.matrix and added the configuration to the environment.matrix item, and came up with:
environment:
matrix:
# Windows job
- job_name: Windows build
appveyor_build_worker_image: Visual Studio 2019
configuration: Release
# Linux job
- job_name: Linux build
appveyor_build_worker_image: Ubuntu1804
configuration: ReleaseNoGui
matrix:
fast_finish: true
build:
project: MySolution.sln
parallel: true
verbosity: minimal
publish_nuget: true
publish_nuget_symbols: false
for:
-
matrix:
only:
- job_name: Windows build
deploy:
- provider: NuGet
name: nuget
which builds Linux with the correct configuration.