Most people play simply get the best gear, defeat the ender dragon... and then what? Create a new world and do it all over again? That gets boring and repetitive very quickly.

So, they turn to mods. Personally, I only VERY recently started looking into mods, and I find myself preferring tweak mods rather than content mods, because there's something nice about the simplicity of Minecraft. Thats the reason we all fell in love with it in the first place.

The key?

Long term progression: specifically looking back on how far you've come, and how much you've accomplished. That, obviously, requires you to stick with one world and not restart and create a new one every month. I have always respected the people who have stuck with the same world for many years, and though I only recently started a long-term survival world (since 1.16), my only regret is not starting sooner.

Build crazy weird things. Leave yourself signs for your future self to find. I have a whole document of ideas that I am constantly adding to, at a rate faster than I can complete them.

Progression!

Minecraft is a project-based game (especially in singleplayer), so find something cool you want to do or make, and go ahead! It's not all about getting gear, it's about creating amazing things! That can be a build, farm, functional base, redstone, anything. Make something to be proud of.
(I personally also really like just exploring/wandering)

first of all find a good seed maybe not to overpowered.
DONT RUSH, take it slowly.
After that build a cool base, Make as many farms as possible, Get god armor (all protection enchantments), explore, get all advancements…
Maybe make the game harder for more challange:
Difficulty -> Hard
Natural Regeneration -> off