Since H2's only waste product after combustion is water, the actual burning of hydrogen is perfectly green. It's the production of the hydrogen that's the problem. Current hydrogen production is mostly by using natgas (I think methane) which produces H2 and CO, plus some other things as byproducts. Green hydrogen is using renewables to power electrolysis to produce hydrogen gas (and oxygen gas) from water.
Since H2's only waste product after combustion is water, the actual burning of hydrogen is perfectly green. It's the production of the hydrogen that's the problem. Current hydrogen production is mostly by using natgas (I think methane) which produces H2 and CO, plus some other things as byproducts. Green hydrogen is using renewables to power electrolysis to produce hydrogen gas (and oxygen gas) from water.