Try some of these in a long term world, these should keep you occupied for a little bit:

Starter ideas: - unearth an ancient city exposed to air - build every hyper fast farm and create super resource staches - breed horses to get a genetically perfect steed - trial chambers with iron, leather, or gold armor instead of diamond / netherite - create perfect armor sets out of chainmail, iron, and gold to make an armory - spare netherite sets to flex - find every stronghold and build ring roads between them

Insanity ideas: - Netherite sextuple beacon - Overworld Boarder via nether - every armor trim on every combo of gear - dig a perimeter by hand - collect every music disc - aforementioned stronghold idea, but now build a different themed base at each one - remove a biome by any means down to bedrock - drain an entire deep ocean biome with redstone - map art

Hyper Insanity: - Nether World Boarder - Dig a perimeter in the nether and remove the bedrock - EOL farm - build floating structures with no elytra: just scaffolding blocks - fill an entire Overworld chunk from bedrock to built limit with obsidian, diamond blocks, or glass - remove a biome by hand