Neat game for the time it was made in. If you had more time or are interested in working on it further, the game suffered from a lack of suspense. The stuff below is only if you are interested in hearing feedback for any possible future post game jam updates.
tl;dr
gotta let the player know that there's a big angler fish early, and use every aspect of the games mechanics to reinforce that the player is in danger.
An example of suspense used in Iron Lung is the lack of a constant view of the outside world, paired with occasional snapshots of something horrible following you around and the audio of it nearby. That, as well as the degradation of the ships hull builds up to the final jumpscare as you know you are in danger, but you can't know when that danger is going to act on you due to the restriction of information.
Your game struggles mostly because the player always knows their relevant surroundings (there's nothing that is implied to be hidden outside of view), and there isn't any threat which seems life threatening that the player knows of through their equipment. Their radar only shows ore veins, so the player can't be scared by any abnormalities as there are never any. The game has coordinates, but they aren't relevant because the player can pilot through the specific tunnels and reach the end through 'following the path' rather than distracting them from piloting with a layer of uncertainty in movement. The game has ore mining, but there is no unique process involved other than grabbing it.
All that is to say, the player is entirely focused on piloting the ship through tunnels, pressing the grab button and twice (quite rarely) having to use tools to fix barely threatening problems. There aren't any stressful activities the player has to perform, or anything on their equipment to show that there is an instantly life ending threat just outside their submarine.
As somebody once said, there's no suspense if a bomb was to just go off under a table when two people are talking, but if you let the viewer/player know that there is a bomb under the table early, then suspense is created as they keep talking near that bomb.
AKA (also the TLDR at the start) gotta let the player know that there's a big angler fish early, and use every aspect of the games mechanics to reinforce that the player is in danger.