How can I activate Office 365 without internet access?

You could quickly connect your computer to the internet using your phone's hotspot feature, either via WiFi or USB. That way you can activate it just long enough to get past the validation check.

I've noticed that Microsoft can be a bit tricky—they want to check online even just to confirm you're offline! If you installed Office another way, maybe you can activate it via phone or check for volume licensing options.

Before diving into the fixes, I’m curious if you're trying to resolve it for just your setup or for everyone in the office? Ideally, your office's tech support team should handle activation issues. If you're in a pinch, sharing your mobile internet can be a lifesaver!

Office 365 typically needs internet for subscription validation. Just so you know, even perpetual versions have started requiring online checks for activation these days. If you ever get the chance to connect, that might help it recognize your license.