@Joekw If you just want to have a profile that can be followed (so you're only serving activitypub JSON, not receiving and parsing anyone else's) then it's relatively easy.
Follow is one of the simpler activities, with little if any variation between implementations. For details, check out https://join.piefed.social/2023/11/18/subscribe-and-unsubscribe-to-a-community-follow/
Sharing the gaming activity would be like making a RSS feed with extra steps and rather than using XML it's JSON.
GNU social JP is a social network, courtesy of GNU social JP管理人. It runs on GNU social, version 2.0.2-dev, available under the GNU Affero General Public License.
All GNU social JP content and data are available under the Creative Commons Attribution 3.0 license.