I had the same problem. Just installed the .deb and I'm running on buster and I accidentally was using the stretch repository. I updated to the buster pgadmin4 repo and now it's loading. Make sure your distro matches the package.
Running Ubuntu 19.4 and installed using packet manager. Got version 4.11-1.pgdg18.04+1
is there a better repo availiable?
pgadmin-support by date:
Соглашаюсь с условиями обработки персональных данных