The Wakemaker is a new gadget: arm-mounted jets that propel the diver and help navigate underwater currents. It is the Subnautica 2 analogue to the Seaglide / Propulsion movement aids of the previous games.
It matters most in current-heavy biomes like the Red Grass Mesa, where flowing currents otherwise dictate where you can go. Personal propulsion also reduces oxygen pressure on long swims between forward bases.