How to install Nintendo Emulator gfceu on Ubuntu 20.04
The best way I found to use snap, because it has later version than ubuntu repos.
sudo snap install fceux-gui --candidate
Than, with 20.04 I have problem "Cannot access file /usr/share/alsa/alsa.conf" And I have found solution, to to accept pulse in snap settings and turn fceux use pulse via SDL settings:
sudo snap connect fceux-gui:pulseaudio :pulseaudio
than run (or create shortcut with this string):
SDL_AUDIODRIVER=pulse fceux-gui
(or you could set for it environment)