There are themed sections on here, but most of the time they are cross-server so things like hashtags (which you can follow) or discussion group accounts (which you can also follow).
Each server does have a "Local" timeline, which on large servers is just a random firehose but on smaller servers is a fun little community feed.
Also, there are non-Mastodon servers on the Fediverse which you can follow such as the Reddit-style Kbin (example server: https://kbin.social).
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