Sharepoint Created Lookup fields ( custom list ) in Documnt Library but on doc loading time not asking to select lookup fields data

did you add this field directly to the list or to Document content type in the list? In first case try to modify Document content type in the list and add lookup field there:

1. at first enable content types management for the list: List settings > Advanced settings > Allow management content types
2. then go to list settings again Content types > Document and add new field there

Hi @Mohammad Qasim ,

This is how the new experience of document libraries works.

To meet your requirement, we suggest you go back to the classic experience for the affected library via library settings> Advanced settings>List experience.

Then Go to Library Settings> Advanced Settings> Click Yes to “Allow management of content types?”

Or go to Library Settings> Find the lookup column> choose Yes to make the field required.

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