You will find a research group within a division to work for. For example, mine was the Computational Earth Science group (since renamed) within the Earth & Environmental Sciences division.
You will be working with a handful (3+) of research scientists as their supporting engineer. On some projects, you may be doing machine learning work in Julia. On others, you may be coding a fluid dynamics simulation in FORTRAN or C++. On others, you might be doing data analytics in Python. It's highly, highly variable, depending strongly on the PIs you're working with, and can change as frequently or infrequently as you wish (within reason).
Ultimately, I did the reverse: went from a DOE lab into a FAANG company. My reasons are particular to me, but if you're at all interested in a slower paced, more varied and collaborative environment, you can't do much better than working for the labs.
For context, at LANL, I was making ~$100,000 / yr with 3 YOE (circa 2019). This is in northern New Mexico, with such a low cost of living that this amount of money goes about as far as $150k+ up in the Boston area (where I am now).