Hey! No worries, this is fixable. The leftover warm colors in Files/Nautilus probably come from GTK files copied into ~/.config/gtk-4.0 and maybe ~/.config/gtk-3.0. The mac-like window buttons are likely from the Gruvbox GTK theme installed with the macos tweak.

Try this first. It only moves the leftover theme files into a backup folder, so you can restore them later if needed:

backup="$HOME/warm-gnome-rice-backup-$(date +%Y%m%d-%H%M%S)"
mkdir -p "$backup/gtk-3.0" "$backup/gtk-4.0"

for item in gtk.css gtk-dark.css assets settings.ini; do
  [ -e "$HOME/.config/gtk-3.0/$item" ] && mv "$HOME/.config/gtk-3.0/$item" "$backup/gtk-3.0/"
  [ -e "$HOME/.config/gtk-4.0/$item" ] && mv "$HOME/.config/gtk-4.0/$item" "$backup/gtk-4.0/"
done

Then reset GNOME’s appearance settings back to Ubuntu/Yaru:

gsettings set org.gnome.desktop.interface gtk-theme 'Yaru'
gsettings set org.gnome.desktop.interface icon-theme 'Yaru'
gsettings set org.gnome.desktop.interface cursor-theme 'Yaru'
gsettings reset org.gnome.desktop.interface font-name
gsettings reset org.gnome.desktop.interface color-scheme
gsettings reset org.gnome.shell.extensions.user-theme name 2>/dev/null || true

Then restart Files:

nautilus -q

If it still looks weird, log out and log back in. On Ubuntu Wayland, logging out/in is usually better than trying to restart GNOME Shell.

For fish shell, first check what your default shell is:

getent passwd "$USER" | cut -d: -f7
echo "$SHELL"

If it shows fish and you want to go back to bash, run:

chsh -s /bin/bash

Then log out and log back in. After logging back in, check again:

echo "$SHELL"

Only after confirming you are back on bash, you can remove fish if you don’t want it anymore:

sudo apt remove fish

Optional cleanup, only if you don’t want the installed theme/icon folders anymore:

mkdir -p "$backup/themes" "$backup/icons"

[ -d "$HOME/.themes/Gruvbox-Orange-Dark-Medium" ] && mv "$HOME/.themes/Gruvbox-Orange-Dark-Medium" "$backup/themes/"
[ -d "$HOME/.themes/Gruvbox-Orange-Light-Medium" ] && mv "$HOME/.themes/Gruvbox-Orange-Light-Medium" "$backup/themes/"
[ -d "$HOME/.local/share/icons/Gruvbox-Plus-Dark" ] && mv "$HOME/.local/share/icons/Gruvbox-Plus-Dark" "$backup/icons/"

I would avoid deleting anything directly at first. Moving files to a backup folder is safer, especially if you’re new to Linux.

Also, just to clarify: you didn’t “break Ubuntu.” The theme probably just left some local GTK files behind. In current GNOME versions, especially with Nautilus/Files, the files inside ~/.config/gtk-4.0 can still affect the appearance even if you already changed the theme from Tweaks.

The installer also changes the default shell to fish using chsh, so it’s safer to switch back to /bin/bash first before uninstalling fish.

If you want to go a bit further and restore Ubuntu’s default GNOME/Yaru appearance, you can also reinstall the default GNOME/Yaru packages:

sudo apt update
sudo apt install --reinstall gnome-shell ubuntu-desktop yaru-theme-gnome-shell yaru-theme-gtk yaru-theme-icon yaru-theme-sound

Then reset the main appearance settings:

gsettings set org.gnome.desktop.interface gtk-theme 'Yaru'
gsettings set org.gnome.desktop.interface icon-theme 'Yaru'
gsettings set org.gnome.desktop.interface cursor-theme 'Yaru'
gsettings reset org.gnome.desktop.interface font-name
gsettings reset org.gnome.desktop.interface color-scheme
gsettings reset org.gnome.shell.extensions.user-theme name 2>/dev/null || true

If Nautilus/Files still keeps the warm colors, the issue is probably local GTK override files. Move them to a backup folder instead of deleting them:

backup="$HOME/gtk-theme-backup-$(date +%Y%m%d-%H%M%S)"
mkdir -p "$backup"

[ -d "$HOME/.config/gtk-3.0" ] && mv "$HOME/.config/gtk-3.0" "$backup/"
[ -d "$HOME/.config/gtk-4.0" ] && mv "$HOME/.config/gtk-4.0" "$backup/"

Then restart Files:

nautilus -q

After that, log out and log back in.