Please see but 135513 concerning the inoperabliity of Dynamic Data Exchange. It appears that the bug report has not been reviewed. I attached a zip file with linked Calc and Writer files that worked in LO6 versions, but do not work in LO7. I have also made simpler linked files in LO7 and still no updating in Writer when data is changed in the linked Calc file.
You created a bug report, so no need to inform users of LibreOffice about this fact. This site is not a communication path to developers and reviews are done on a voluntary basis based on availability of developer resources, interests, severity and whatever other factors … This is a non-commercial free and open source project.
Regarding the question: LibreOffice 7.0: Release Notes does not contain any information regarding changes in DDE functionality.
Update: There is another bug report [#tdf135676](https://bugs.documentfoundation.org/show_bug.cgi?id=135676) which might be a duplicate and has been reviewed. May be you could leave a message there.