Most advice about optimizing a Twitch profile is a list of things to fill in, with no explanation of which ones change anything. This is the shorter version: the settings that have a documented effect on how your stream is shown, and the standard for each.
The settings Twitch actually reads
Tags. Tags appear next to your thumbnail, title and category everywhere your stream is shown. Viewers filter the browse directory by them, searching a tag puts channels using it at the top of results, and Twitch uses them to recommend streams to people who have watched similarly tagged ones. Twitch allows 10 custom tags plus an automatic language tag. Most guides still say 5, because that was the cap until August 2022.
Language. Your broadcaster language becomes a tag automatically and viewers filter by it. Set wrong, you are shown to people who cannot follow along.
Category. This decides which directory you are listed in. It is the largest single input into who could find you by browsing.
The parts that work while you are offline
You are live a few hours a day. Your channel exists for all of them, and most first-time visitors arrive when you are not streaming.
Your offline banner fills the video player when you are not live. Blank reads as abandoned. Put your schedule and where else to find you on it.
Panels sit under the player and stay visible whether you are live or not. Three is enough: who you are, what to expect, where else to find you.
Your bio is most of what an offline visitor gets. What you play, when you are live, one reason to stay. Two or three sentences.
One working link. A Discord invite beats a social feed, because people can talk to you there. Check it still opens.
What this does and does not do
A well set-up channel does not make people arrive. It makes the people who do arrive able to work out who you are and how to come back. Those are different problems, and mixing them up is why "I optimized everything and nothing happened" is such a common experience.
If you want to see where your own channel stands rather than working from a list, Channel Check scores it across 16 checks and tells you the standard for each one.
The wider context is in the Channel Optimization guide.