The Real Driving Simulator Subreddit
Popularity: 
The Real Driving Simulator Subreddit is one of the most popular communities for the Gran Turismo Series, where you can find news, commentary, rumor, garage collection, tips and tricks, images, and anything else!
The forum has over 130,000 members. It's highly active. For instance, a post on "the weekly discussion thread received 200 comments.
GTPlanet Gran Turismo 7 Forum
Popularity:
GTPlanet Gran Turismo 7 Forum is a very popular community of the game.
Besides online discussions, the forum also offers an ultimate guide, leagues & online racing, photo mode & scapes, car tuning, car liveries & livery editor, and more,
You can find lots of useful information about the game by browsing the posts, like the engine swap compatibility list, the credit cost of all cars, the master car list, frequently asked questions, and the master track list.
When we visited the forum, we found the community was active and the users were generally friendly. Some posts received lots of replies. For example, a post of Gran Turismo 7 bug report received over 2000 replies.
If you have a question about the game, or just want to interact with other players, we think the forum is a good starting point.
Gran Turismo 7 Subreddit
Popularity: 
Gran Turismo 7 Subreddit is another popular subreddit for the game. The subreddit has over 13,000 members.
You can find some interesting information about GT7. For instance, there's a poll on "whether you like Gran Turismo 7 or not", with over 950 votes.
Gran Turismo Official Community
Popularity:
Gran Turismo Official Community is a place where users interact with others.
In the community, you will find scapes photos, race photos, decals, car livery, helmet livery, suit livery, and replays.
Gran Turismo Facebook
Popularity: 
Gran Turismo Facebook is the official page for the PlayStation-exclusive game series, "Gran Turismo".
The page is popular with 2,400,000 followers. An announcement of an incoming update of the game has 2,300 likes, 500 comments, and over 200 shares.
Since it's the official page, only the official account of GT can make new posts. However, all users can like, comment, or share them.
RaceDepartment Gran Turismo Forum
Popularity: 
RaceDepartment has a subforum for Gran Turismo.
The forum isn't very active. We only found three new posts for the last month.
TrueTrophies Gran Turismo 7 Forum
Popularity:
TrueTrophies has a subforum for Gran Turismo 7.
We find the subforum isn't very active. We found only 2 posts started within the last 2 months, and each post had no more than 3 replies.
Fanatec Gran Turismo Forum
Popularity:
Fanatec has forum for Gran Turismo.
The forum isn't very active. The discussions are related to how to use Fanatec hardware in the game.