Sometimes Structured doesn’t show up as a widget option in your widget gallery. This issue is commonly caused by Apple.
First of all, please ensure that your Structured app and iOS are up to date on your device. Usually, this issue can be resolved by restarting your device.
Structured Widget is still missing
As a last resort, you could try to delete and reinstall the Structured app. Please ensure to create a Backup before doing so, as this step might delete all of your data in Structured.