if your rosegarden is crashing when loading *.rg (rosegarden files) then delete the following configuration files.
you can search for these files buy using this command in terminal:-
find ~ -name "rosegarden"
And you will see these files in you home directory (example):-
/home/NAME_OF_HOME_DIR/NAME_OF_DIR/.kde/share/config/rosegardenrc
/home/NAME_OF_HOME_DIR/.config/rosegardenmusic
/home/NAME_OF_HOME_DIR/rosegarden
/home/NAME_OF_HOME_DIR/.local/share/rosegarden
Just delete them and restart rosegarden.
You can install the latest rosegarden (20.6) if you keep getting the same crashes. It should fix the problem crashes.
You need Cmake and other cmake modules if you are to compile rosegarden. Ask for help for other contingencies.