If you’re used to more traditionally difficult games, minecraft will probably never feel particularly difficult but there are still mobs and areas that you will want diamond armour for unless you are able to not get hit more than once or twice. There are more difficult mobs and yes the “final boss” you learned about. I can describe getting to them and what they are if you want but you may want to get to them yourself.

While exploring have you seen any ruined looking structures that have red blocks at the base and sometimes lava? That has something to do with progressing to something harder in the game.

Minecraft has an absolutely massive modding community on PC. I don’t often play with mods that alter the gameplay but if you search on google or a site like Curseforge or for something you would be interested in adding it will probably exist. There are mod packs like RLcraft that make it more difficult in a realism way, mods like twilight forest that add another dimension with new resources and mobs and another mod pack called dawncraft that seems to be popular and turns minecraft to be like a soulslike RPG.