It is not ‘Dia’, but rather ‘dia’
# dnf list installed dia*
Installed Packages
dia.x86_64 1:0.97.3-17.fc34 @fedora
dia-CMOS.noarch 0.1-18.fc34 @fedora
dia-Digital.noarch 0.1-18.fc34 @fedora
dia-electric2.noarch 0.1-18.fc34 @fedora
dia-electronic.noarch 0.1-18.fc34 @fedora
dia-gnomeDIAicons.noarch 0.1-17.fc34 @fedora
dia-optics.noarch 0.1-18.fc34 @fedora