If someone hasn’t asked “what can I use instead of Windows?” then “use Linux” is unsolicited advice. If you absolutely can’t stop yourself from suggesting Linux every time someone wants to complain about using Windows—something they might not even have a choice in, if their job requires it—at least suggest something useful for their Windows problem. Some jackass rolling by when you have a flat tire and saying “you should have taken the bus” isn’t offering helpful information, they’re being an asshole.
Unsolicited advice is asshole-behavior, like it or not.
It’s not unsolicited though, the thread OP is referring to was complaining about people suggesting Linux in response to complaints about Windows.
If someone hasn’t asked “what can I use instead of Windows?” then “use Linux” is unsolicited advice. If you absolutely can’t stop yourself from suggesting Linux every time someone wants to complain about using Windows—something they might not even have a choice in, if their job requires it—at least suggest something useful for their Windows problem. Some jackass rolling by when you have a flat tire and saying “you should have taken the bus” isn’t offering helpful information, they’re being an asshole.