The dnf group list command will list both installed and available package groups in the repositories you have installed. 

dnf group list

Something like this will be returned, which shows the available and installed package groups.

Available Environment Groups:
   Fedora Custom Operating System
   Minimal Install
   Fedora Workstation
   Fedora Cloud Server
   KDE Plasma Workspaces
   Xfce Desktop
   LXDE Desktop
   LXQt Desktop
   Cinnamon Desktop
   MATE Desktop
   Sugar Desktop Environment
   Deepin Desktop
   Development and Creative Workstation
   Web Server
   Infrastructure Server
   Basic Desktop
   i3 desktop
Installed Environment Groups:
   Fedora Server Edition
Installed Groups:
   Headless Management
Available Groups:
   3D Printing
   Administration Tools
   Audio Production
   Authoring and Publishing
   C Development Tools and Libraries
   Cloud Infrastructure
   Cloud Management Tools
   Compiz
   Container Management
   D Development Tools and Libraries
   Design Suite

The dnf group list available command can also be used to list only installed packages.

dnf group list available

The dnf group list installed command can be used to only liste the installed package groups.

dnf group list installed

The -v or --verbose flag can be included to list the repositories you have installed at the beginning of the output. It is very common to install the EPEL (Extra Packages for Enterprise Linux) repository.

dnf group list --verbose

Something like this should be returned. Notice 'using cache". The cache is found at /var/cache/dnf. The dnf clean all command can be used to clear the cache.

repo: using cache for: fedora-cisco-openh264
fedora-cisco-openh264: using metadata from Mon 22 Feb 2021 06:49:00 PM CST.
repo: using cache for: fedora-modular
fedora-modular: using metadata from Fri 23 Apr 2021 05:25:38 AM CDT.
repo: using cache for: updates-modular
updates-modular: using metadata from Wed 19 May 2021 08:20:13 PM CDT.
repo: using cache for: updates
updates: using metadata from Sun 23 May 2021 07:53:21 PM CDT.
repo: using cache for: fedora
fedora: using metadata from Fri 23 Apr 2021 05:47:57 AM CDT.

The -v or --verbose flag will also include the group ID in parathesis in the output.

Available Groups:
   3D Printing (3d-printing)
   Administration Tools (admin-tools)
   Audio Production (audio)
   Authoring and Publishing (authoring-and-publishing)
   C Development Tools and Libraries (c-development)
   Cloud Infrastructure (cloud-infrastructure)
   Cloud Management Tools (cloud-management)
   Compiz (compiz)
   Container Management (container-management)
   D Development Tools and Libraries (d-development)
   Design Suite (design-suite)
   Development Tools (development-tools)
   Domain Membership (domain-client)
   Fedora Eclipse (eclipse)