Assembly sure, since it will differ from ISA to ISA. But C is still a "high" level language in the sense that you can write once run "anywhere". Also, more work to do something is expected since C is such a "bare" language to simplify. But again, it doesn't count as it not being as accessible to get new developers started, but it is and will be more cumbersome to work with (in the context of redis like software).

So yeah, maybe it depends on how you would define accessible is. I think if it is defined as just "how easy it is to get started and understand how it works, and how to work with it", C and C++ is quite accessible with a good teacher/mentor. The teacher/mentor is important in C and C++ because unlike C# which has Microsoft as its main authoritative source and the big influencer in the language, C and C++ doesn't have those so the resource on learning it can vary wildly.

I think C is way more accessible than C++. It's such a simple language that there are only so many footguns. C++, on the other hand, is a behemoth, and there are so many different opinions on "the right way" that it can be quite confusing. And with C++, you get all the baggage of C, and a bunch more.

With C#, you don't need to worry about memory as much, virtual tables are more sane, templates are more sane, etc. Basically, C# is what happens when someone adds a GC to C++ and cleans house. It's still complex, but there are far fewer footguns and a vibrant community. The C++ community is large, but I wouldn't call it "vibrant."