Explaining C++ lookup rules or convincing a teammate that a particular piece of code contains undefined behavior... it helps to be in person. I haven't tried this sort of work over video chats, though.
That can't be explained over email? How do the LKML people handle this?
My last Django project, a remote developer had the app up and running in their environment and was fixing bugs before lunch to get a feel for our code.
C/C++ jobs tend to be more more like the former than the later. Many C/C++ jobs are not even possible to do remote; the last time I managed a C programmer it was for an application appliance and I would have had to ship them prototype hardware if they were remote.
I also helped hire and support a consultant who was updating some C++ drivers for some proprietary hardware we had. He never actually came into the office, I just shipped him the device, supporting software, and emailed instructions.
So it's definitely possible to do, but it isn't the easiest type of job to get, especially if you can't visit the premises at all.
For the OP, I'd suggest relaxing your preferences on what type of code/language you want to write for now. Try to find a job doing something you already have the most experience in, but at a company that either has the C++ projects that you're interested in, or seems likely to have connections to companies that do that. Once you establish your competence with them, you may find it easier to switch over to C++ while still being all remote.
If I look at actual sit in office jobs.. I see something like
Java > PHP > .NET > Node > Ruby...
but if I look for online jobs, I see something like
Ruby > Node > <sharp dropoff> > Java??
Sure it changes by area for the local job breakdown.. but while trying to find a remote job, I sometimes regret being a Java/Scala guy instead of a Ruby guy. (But when my code doesn't take 300 servers to run on due to Ruby perf, I am sure that regret will soon fade).
I have a feeling it has to do with the general demographics of those languages users. Python/Ruby/Node positions would be mostly filled by young people working on web stuff (so they're more open to remote work), and Java positions would mostly be in BigCorps with a more traditional organization. But that's just a conjecture.
The comment about performance made me chuckle (Most of my colleagues work with PHP)