What you’re seeing usually happens when something is blocking Steam’s connection to the authentication servers, so the client can’t even get to the stage of sending a Steam Guard code. Since it works on your Mac and web browser, your account and credentials are fine — the issue is with the apps on those other platforms.

A few things to try:
– Check your network/firewall/VPN: Make sure Steam isn’t being blocked by a firewall or VPN. Try logging in on another network (like mobile hotspot) to see if it works.
– Time/date sync: Steam login can fail if your device clock is out of sync. Double-check your Windows, Linux, and iPhone have the correct system time and are set to auto-sync.
– Clear download cache / reinstall: On Windows and Linux, clear the Steam client’s download cache (Steam > Settings > Downloads > Clear Cache). If that doesn’t work, reinstall the client.
– Test on iPhone: If the iOS app still won’t log in, uninstall/reinstall it, and make sure you’re downloading the official “Steam Mobile” app from Valve.
– Two-factor/Steam Guard: Since your account prompts for a code on Mac, Steam Guard is active. If the app doesn’t even ask for the code, that means the connection is failing before that step.

If nothing works, it’s best to contact Steam Support directly — choose “Can’t sign in > Steam Client Login” and list the platforms you’ve tested. They can check if there’s a block or security flag on your account that prevents login from new devices.