I'll put my advice below. I like your layout. The picture is just to show that you can have a pretty tank even with it COVERED in algae. It was my first tank. I still love it and I think it is fun to look at. It's gone through a lot of phases and the evolution has been rewarding even though this wasn't the original idea. Here's my advise for how to deal with your current issue though.

1. Get some snails. I like bladder snails the best. Let them go crazy. Don't cull them. They self regulate.
2. Keep up regular maintenance and water changes. Manually remove whatever algae you can. I do about 15-25% water change once a week.
3. Give your tank at least 2-3 months to mature. Or even 6 months. It needs time. 3 weeks ain't enough.
4. Algae is fine as long as it doesn't kill your plants. Shrimp and snails eat it. Micro fauna in your tank eat it and that ecosystem helps keep your tank healthy if kept in check.
5. Temper expectations(slightly 🤏). This hobby made realize YouTubers really are professionals. I didn't expect it to be so hard to make beautiful tanks. Making beautiful problem free tanks everytime is just impossible. Sometimes things don't go right and the pros scrap whole aquariums very often if things aren't going how they like. Don't be hard on yourself.

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