My understanding is that deep-sea nodules produce oxygen by a process similar to electrolysis, where they generate currents that split seawater into hydrogen and oxygen.

The proportion of global abiotic and global total oxygen production this represents is not known, but may be significant.

Leaving aside the certainty of yet more cascading collapses of marine life in waters de-oxygenated by deep sea mining: do we want to risk finding out the hard way how significant?

Apparent consensus is we do, but I don’t have to like it, or think these are the plans of sane people who see the big picture.