One challenge was that, while we were lucky to score some talented systems engineers who joined dev teams, it wasn't easy to communicate to leadership that owning and managing infrastructure from the public internet all the way into the database requires knowledge and experience that software engineers might not have.
I tried putting together a PluralSight channel for us to use internally to help onboard new team members. We had access to AWS sandbox accounts where we had no proprietary data, and could build infra as needed to learn and/or experiment with ideas/designs/new services.
You can target people with this experience when hiring, but just getting qualified devs was hard a year ago, let alone people who also had systems experience/knowledge. A lot of the candidates worked somewhere with a QA team who tested their code, a dev ops team who managed a CI/CD process and managed releasing their code, a database team who owned the database cluster, a networking team who owned networking infrastructure, etc.
Really what you're looking for is somebody who likes to code, but also is interested in systems enough to at some point go read the RFC, run Wireshark, etc. I know a little about networking because I ran my own firewall on OpenBSD years ago, have been hosting e-mail and web for over 20yrs, etc. We got lucky with a few hires who lived and breathed code and systems engineering, but it will be challenging to retain people like that in a hot market.
At the end of it all, I couldn't really come up with a way to effectively accelerate learning these skills and getting that experience.
I started the same day as a new grad, and will never forget when, at the end of the day, he said "you mean I have to keep learning?" Yes, yes we do. Still do.
edit: I'd be interested in working on putting content together if people think it would be valuable.