In an ideal world, solution architects are really your most senior design engineers, have long-term plans for how the sum total of your businesses IT systems fit together, and steer development, acquisition, and upgrades across all aspects (clients, network, back-end, in-house code, cloud etc) to turn those long term plans into reality.
Without that view, a businesses IT landscape will lack cohesion resulting in higher cost, complexity, and risk. Done well, architecture can keep all those things at better levels as well as serving as a bridge between the technical world and management that often doesn't have the domain knowledge to understand the implications of the choices they make. Likewise engineering (whether software, infra, or network) likely don't have an agreed view of all the stuff outside of the tech itself and architecture is a place for that to be considered. Stuff like what support processes and staffing needs to look like and how it will be funded, or ensuring that some compliance gotcha coming down the pipe in five years time won't conflict with some technical minutiae being planned for right now and likely to still be there, or utterly essential, when that five years comes to pass.
Now, that said that's just my personal interpretation and the role is interpreted quite differently from org to org. I probably won't re-enter the field because I have a dim view of architects that sit exclusively in the abstract conceptual realm all day long and don't/can't roll their sleeves up to design and deploy tangible systems and services any longer. The longer anyone spends in that abstract space, imo the more useless, self-serving, and eventually actively harmful their output becomes. Solution design and infrastructure deployment (storage, networking, client, systems management layer stuff) is more my speed but that realm is being eaten up by cloud in the SME space where individual contributions actually matter.