When you copy a table from a Google Sheets spreadsheet and paste it into a Google Docs document, you get this option:
After you click Paste, if the copied table has Google Sheets checkboxes (from Insert> Checkbox), it'll show up in the linked Google Docs table as "TRUE" or "FALSE", depending on whether the checkbox is checked or not in Google Sheets. So Google Sheets' checkboxes do not display properly in Google Docs.
One kludgey solution would be to create add helper cells next to the Google Sheets checkboxes that convert them into Unicode checkboxes, e.g.:
=IF(A1, "☑", "☐")If that formula's in column B, you'd then copy from column B (with Unicode checkboxes) instead of from column A (with Google Sheets checkboxes).
However, is there a way to avoid this kind of kludge and get Google Sheets' native checkboxes to show up directly in linked tables in Google Docs?