Oh, honey. You're out here trying to sell T-shirts like they're medicine for a disease no one has. Stop treating them like a product with a conversion goal - they're fabric with a logo, not a life support machine.
The product is the brand. Always has been.
Pick three groups you reckon would actually want to wear your stuff and go stalk them IRL. Not in a creepy way - find where they hang out, eavesdrop, ask dumb questions. Then choose one. One. Smother them in your brand like it's the only blanket in a blizzard. Collab with the influencers they already worship, invest in visuals that make people think I need to be in that photo, and make your brand their identity.
Go read about the 1980s jeans wars - Guess, Calvin Klein, Levi's, Wrangler. None of them sold denim. They sold a feeling. You're selling a T-shirt. Fix that.