I really love bright, stained glass builds. Like an ocean with coral made out of glass with the brightest colours you could ever imagine. Maybe a sunken ship and other little details like that.
I personally love to see organics, they are difficult and take a lot of practice, but they are used in almost all designer builds so it would be good for you to have them in your portfolio. Also build some maps, there is a map submission subforum so try to build some stuff and be active in there, it should also help you.
purely for showing off your building ability, I would suggest doing either a minerware map or an FFA map (probably java but i dont use bedrock so idk how it work there) here is the thread with info: https://www.cubecraft.net/threads/keep-this-in-mind-when-building-a-map.223640/Hmm. I will try to make a map. Got any ideas for what Minigame? And version (Java or Bedrock)?