I have a multi folder workspace project.
At the moment when I use > Arduino: upload it always uploads the master.ino.
How can I upload the other file?

Currently, we do not support multi-workspace well, the extension will only work for the first folder contains arduino.json file. We will support multi-workspace in the later version.
As a workaround, you need open slave folder instead of workspace.
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Currently, we do not support multi-workspace well, the extension will only work for the first folder contains arduino.json file. We will support multi-workspace in the later version.
As a workaround, you need open slave folder instead of workspace.