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