Check out a list of things to build. There's plenty on Planet Minecraft and also on google. This list on EnderChest is handy to use.

Time for a brianstorm!

Midevil castle in space
A Spaceship carrying Cheese to the moon
Re-create Elon Musk's car in space
Create a Command-block based Minigame for Realms
Create a snowy forest and hide loot inside for players to find
create a dungeon, but you're only allowed to use 3 blocks.
Create a boss-fight against a giant and EVIL duck!
Create a duck in space
Make a hospital that can lure different hurt mobs in and heal them.
Create an automatic sheep farm that Only takes the wool.
Make a sorting system for blocks
Create a house, but build it with your screen turned up-side down :D
Make a statue of Star Butterfly from: Star Vs. The Forces of Evil
Create a magic wizard that uses a gun instead of a wand.
Re-create real or game based guns in minecraft!
Create your own Build-bundle for everyone to use!
Make an awesome pawn shop where villagers can buy useless items!
Make a UFO that isn't round, nor an actual spaceship
Create a flying Van with the words: This is not a Van on the side
Create a savanna filled with coffe shops!

aaand my brain just went dead. Hope you'll find at least some inspiration from my brainstorm:D

I say just build a tower made of stone and cobblestone and brick stone with glass.
Build a cobblestone generator.
Build a auto weat farm.

build any structure and try using electrics.
I mean give it a go.

Build something from your favorite tv show / movie / book, or build something such as a monument near you.

fidget spinner /s

I get bored by them

You can build a simple house if you like... idk.