Of course, however, it is a terminology that tells the package manager to install a certain group of packages (in this case they correspond to the main set of LibreOffice apps except Base).
Yes. However, I do not know the status of your system, since previously you may have installed or removed packages manually, so I recommend uninstalling all the packages related to LibreOffice with dnf groupremove "LibreOffice"or more aggressively with dnf remove libreoffice* (check the list of packages well before confirming). Then you can install the group of packages through the groupinstall command or each individual package that you need.
There is no such thing as “main app”, since LibreOffice is a single binary with modules. Maybe you refer to the “Start Center”. Even if you install a single app, you can use the Start Center (if you installed LibreOffice correctly you will be able to see the desktop launcher) or run soffice in the terminal without any parameter.
I wonder if you had installed AOO by downloading the RPM packages from the web, you did not do the same with the RPM packages of LibreOffice if you had that issue or have installed the app that you needed with a dnf install libreoffice-math libreoffice-writer libreoffice-draw … etc .
Cool.