In similar vein, I had no desire for the “Gnome Classic” – already in el7. I did found out that that particular desktop is offered by package gnome-classic-session, so I exclude that from my package lists.
What does it have?
$ dnf -q rq -l gnome-classic-session
/usr/share/glib-2.0/schemas/00_org.gnome.shell.extensions.classic.gschema.override
/usr/share/gnome-session/sessions/gnome-classic.session
/usr/share/gnome-shell/modes/classic.json
/usr/share/gnome-shell/theme/calendar-today.svg
/usr/share/gnome-shell/theme/classic-process-working.svg
/usr/share/gnome-shell/theme/classic-toggle-off-intl.svg
/usr/share/gnome-shell/theme/classic-toggle-off-us.svg
/usr/share/gnome-shell/theme/classic-toggle-on-intl.svg
/usr/share/gnome-shell/theme/classic-toggle-on-us.svg
/usr/share/gnome-shell/theme/gnome-classic-high-contrast.css
/usr/share/gnome-shell/theme/gnome-classic.css
/usr/share/wayland-sessions/gnome-classic-wayland.desktop
/usr/share/xsessions/gnome-classic.desktop
It is actually the *.desktop files that are used in the menu.
Now, ask yourself, who has them and/or which ones you have installed:
$ dnf provides /usr/share/\*sessions/\*.desktop
$ rpm -qf /usr/share/*sessions/*.desktop
The trivial solution should be to remove the packages (and hence files) that you don’t want. For Gnome you probably can do that. For Fluxbox, … after card “works”?
What is left on the menu after those are gone?