My fish is blind? (fish does not recognise any commands after setting it as default shell on Mac OS Big Sur, M1 Mac)

I installed fish with homebrew on Mac OS Big Sur, Apple Silicon. Then I added /opt/homebrew/bin/fish to /etc/shells. When I now start fish from the default shell, it recognises all commands (like git flow init).After changing the default shell with chsh -s /opt/homebrew/bin/fish, suddenly it won't recognise anything anymore and always gives a Unknown command.I haven't found anything regarding this issue and uninstalled fish and brew several times...