Your Family Type files may not work in Revit 2021 because Autodesk renamed several unit types. If you’d like a free tool to update your type files – here it is.
After this tool changes your family type files, those files won’t work in older versions of Revit because of the unit type renaming.
Ideas Forum post
The Building Coder post
https://thebuildingcoder.typepad.com/blog/2020/04/revit-2021-unit-types-family-type-catalogues.html
Help file