Almost nobody using C (or C++ for that matter) has read the standard. The standard exists for compiler developers. If you want to read the standard, you can get copies of the drafts for free. It is an open secret that the final draft is basically verbatim with the standard that costs money. However, it is very rare that a C programmer needs to read the standard.

As for C++, there is nothing at that link that says you need a textbook to learn C++ (and the idea that you need one is ludicrous). The textbooks are suggested resources. There are plenty of free resources available online that are just as good for learning C++.

You would be better off learning C before learning C++. C++ is a huge language and its common history with C means that if you do not understand C, you are likely going to be lost with C++. If you insist on learning C++ first, here is the first search result from DuckDuckGo when I search for "learn C++":

https://www.learncpp.com/

You will likely find many more.

For what it is worth, when I was young and wanted to learn C++, I had someone else tell me to learn C first. I had not intended to follow his advice, but I decided to learn C++ by taking a university class on the subject and the CS department had wisely made learning C a prerequisite for learning C++. I later learned that they had been right to do that.

After learning C++, I went through a phase where I thought C++ was the best thing ever (much like how you treat Rust). I have since changed my mind. C is far better than C++ (less is more). I am immensely proud of the C code that I have written during my life while I profoundly regret most of the C++ code that I have written. A particular startup company that I helped get off the ground after college runs their infrastructure on top of a daemon that I wrote in C++. Development of that daemon had been a disaster, with C++ features making it much harder to develop than it actually needed to be. This had been compounded by my "use all of the features" mentality, when in reality, what the software needed was a subset of features and using more language features just because I could was a mistake.

I had only been with the startup for a short time, but rejoined them as a consultant a few years ago. When I did, I saw that some fairly fundamental bugs in how operating system features were used from early development had gone unresolved for years. So much of development had been spent fighting the compiler to use various exotic language features correctly that actual bugs that were not the language's fault had gone unnoticed.

My successor had noticed that there were bugs when things had gone wrong, but put band-aids in place instead of properly fixing the bugs. For example, he used a cron job to restart the daemon at midnight instead of adding a missing `freeaddrinfo()` call and calling `accept()` until EAGAIN is received before blocking in `sigwaitinfo()`. Apparently, ~3000 lines of C++ code, using nearly every feature my younger self had known C++ to have, were too complicated for others to debug.

One of the first things I did when I returned was write a few dozen patches fixing the issues (both real ones and cosmetic ones like compiler warnings). As far as we know, the daemon is now bug free. However, I deeply regret not writing it in C in the first place. Had I written it in C, I would have spent less time fighting with the language and more time identifying mistakes I made in how to do UNIX programming. Others would have been been more likely to understand it in order to do proper fixes for bugs that my younger self had missed too.