Here are all the GNOME Core Apps I could find on Flathub.

• Audio Player flatpak install flathub org.gnome.Decibels
• Calculator flatpak install flathub org.gnome.Calculator
• Calendar flatpak install flathub org.gnome.Calendar
• Camera flatpak install flathub org.gnome.Snapshot
• Characters flatpak install flathub org.gnome.Characters
• Clocks flatpak install flathub org.gnome.clocks
• Connections flatpak install flathub org.gnome.Connections
• Contacts flatpak install flathub org.gnome.Contacts
• Disk Usage Analyzer flatpak install flathub org.gnome.baobab
• Document Scanner flatpak install flathub org.gnome.SimpleScan
• Document Viewer flatpak install flathub org.gnome.Evince
• Extensions flatpak install flathub org.gnome.Extensions
• Fonts flatpak install flathub org.gnome.font-viewer
• Image Viewer flatpak install flathub org.gnome.Loupe
• Logs flatpak install flathub org.gnome.Logs
• Maps flatpak install flathub org.gnome.Maps
• Music flatpak install flathub org.gnome.Music
• Text Editor flatpak install flathub org.gnome.TextEditor
• Videos flatpak install flathub org.gnome.Totem
• Weather flatpak install flathub org.gnome.Weather
• Web flatpak install flathub org.gnome.Epiphany

Command to uninstall native apps from Arch Linux

$ sudo pacman -Rs decibels gnome-calculator gnome-calendar snapshot gnome-characters gnome-clocks gnome-connections gnome-contacts baobab simple-scan gnome-shell-extensions gnome-font-viewer loupe gnome-maps gnome-music gnome-text-editor totem gnome-weather epiphany