Hi,
Thank you for sharing your question. I understand your concern, and I appreciate the detailed explanation. It can be frustrating when an input method you need is unavailable.
The reason you cannot use Microsoft Changjie or Microsoft Bopomofo is that the language features for Chinese (Traditional, Taiwan) have not been fully downloaded. The warning message indicates you are on a metered network, which prevents Windows from downloading additional language components required for these input methods. This is normal behavior and does not mean the feature is removed.
To resolve this, connect to a non-metered network (such as standard Wi-Fi without data limits), then go to Settings → Time & language → Language & region → Chinese (Traditional, Taiwan) → Language options and download the missing language features. Once installed, the input methods will become available.
I hope this helps.
Best Regards,
Noel