The Wave Beam, the final beam upgrade in Metroid Dread, is necessary to complete the game. The Wave Beam allows Samus to fire beams through walls and enemies alike, triggering explosions to open new pathways. To obtain the Wave Beam, you need to contend with the game’s final and most challenging EMMI.
Head to Ferenia, in particular, the area located below:
Once you’ve defeated the Central Unit miniboss, you will have to escape out into the EMMI Zone, where a small gauntlet will await you. Unlike other EMMI encounters, you cannot just blast away immediately and win. You will need to blow up Bomb blocks, Wide Beam Blocks, and Phase Shift through pressure plates to reach a long enough hallway. Once there, you can post up and use your Omega Blaster to melt the carapace, and the Omega Cannon to destroy the EMMI.
The Wave Beam is now yours, and you can freely reach most areas in the game — the purple door covers found in most late-game areas can now be destroyed. The only upgrade left to find is the Power Bomb over in Hanubia, so start making your way over for the final stretch of the game.