They can't even push out a single biome update in under 1.5 years, so I wouldn't rely on the devs to add difficulty. As usual, modders have added more to the game than the devs, which is pathetic if we're being objectively honest here.

If you want to up your game, try any or all of the following:

Creature Level and Loot Control[valheim.thunderstore.io]
MonsterLabZ[valheim.thunderstore.io]
RRR Monsters[valheim.thunderstore.io]
RRR NPCs[valheim.thunderstore.io]
RRRBetterRaids[valheim.thunderstore.io]
Custom Raids[valheim.thunderstore.io]

This is just a handful of modded content that is out there, but is enough to prove the dev's ineptitude in creating their own.