The problem is that those developers are also going to forget to update the ignore-by-default .gitignore to allow files, so there will be missing files. And they won't see any problems, because it works on their machine.
It's often said that you can't fix behavioral problems with technology, but I've found that tooling that strictly enforces rules is really useful.
Yeah command line is cool and all but I do believe most of the developers should be using UI tooling where staging area is showing nice diffs.
Built in GIT handling in IDE usually is better than command line but also usually worse than dedicated tool like GitExtensions or SourceTree which are free and are super convenient for staging.
People don't know they don't have to stage whole files but they can stage hunks, well in command line it is too much hassle for me but in GUI tools it is no brainer.
I recommend looking here: https://git-scm.com/tools/guis
(it might be that you will be waaay cooler using GUI tool because you will be able to fix things others can't ... saying from my experience)
Fun fact: Jonas, the creator of tig, is an ex-colleague of mine. It’s cool working with people while using dev tools they wrote!
Plus, it's not the worst idea to exercise your "whoops we leaked our secrets" procedures. You do have procedures, right?
But I'm a little worried that solo developers might follow this device. And then not notice for weeks or months, losing large amounts of git history in the best case; Or potentially massive amounts of actual work if their original development folder is gone.
Not pushing a file has a much easier fix than pushing an API key. The damage is also very different.
Sure, both have failure modes but the effect of the failure is different and acting like they're the same isn't helpful to finding solutions