Just found out that the lovely #OnlyOffice does not have a "Fill Down" function. This lovely person wrote that plugin for OnlyOffice: https://github.com/une4s/onlyoffice-fill-down
GitHub - une4s/onlyoffice-fill-down: Fill Down plugin for OnlyOffice

Fill Down plugin for OnlyOffice. Contribute to une4s/onlyoffice-fill-down development by creating an account on GitHub.

GitHub