Yes but it's not one or the other - there's million different things to do in software before getting to the level of building blockchain crap.

Also I'm really curious what people consider valuable environmental work - like, if you didn't have to work for money tomorrow, what kind of environmental work exactly would you take on?

Realistically, I think unless you are going to work on some hugely disruptive product, your best bet is probably something like local politics, as unfortunate as that is.

For example, in my area I would probably push for the local mangrove coast line to be protected from development. Or perhaps for my county to ban or somehow restrict two-stroke engine use.