From the looks of it, no.
Flathub package: Flatpak LibreOffice 6.1.* vcl stuck with GTK on KDE Plasma and won't work with Global Menu · Issue #63 · flathub/org.libreoffice.LibreOffice · GitHub
Fedora flatpak is built with libreoffice-gtk3 but not libreoffice-kf5.