For Electrum testnet on Windows OS:
Right-click the Electrum shortcut; In the Properties-Shortcut, edit the Target column by adding the following text at the end:
Although, I am using Windows OS. On my laptop, which was window 10, I noticed when I downloaded Electrum on it when I bought it 2 years ago or so, the testnet was created automatically.
I got another laptop running Window 11 which I have just downloaded Electrum on recently which you can see from above image. The testnet also was created automatically.
That's the shortcut pre-generated by the installer (
setup) version of Electrum Windows binary.
But for "
stand-alone" and "
portable" versions, the command line option should be provided like in other operating systems or create a shortcut like instructed by Husna QA.