There is no algorithm on Pixelfed, it's entirely up to you to decide what goes in your timeline. One of the best ways to fill your timeline with stuff you're interested in is to follow hashtags:
1. Search for a hashtag remembering to include # at the beginning
2. Choose the hashtag you want from the list of suggestions
3. Click the "Follow" button at the top
Once you've followed a hashtag, posts with that hashtag will gradually start to appear in your timeline even if you don't follow the person who made it.
If you want to keep track of your followed hashtags go to Account Settings > Relationships > Hashtags
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