My experience (in the US) is that the standard is 90%+ is an A, 80-90% is a V, 70-80% is a C, etc.

Individual profs will change it around if that specific class is easier/harder than others. The only classes I've had where an A started at 92% or 93% were classes that were less exam based and based more on essays, portfolios, presentations and the like. Often professors are generous with points in those sorts of classes and adjust the grading system accordingly.

On the flip side, I've also had classes where an A started anywhere between 85% and 90%. These were usually more challenging classes with tough exams.

There are also many professors who keep the standard 90%+ as an A but curve it so that the average grade is a C. These professors choose to give challenging exams where most students get a 50% or so, and the range may be from, say, 25% to 75%. The professor then just tacks on 25 points to everyone's score so that most people get a C, and few fail, and a few get an A. This, I think, roughly reflects how other countries do it, accept instead of calling a 70% an A, they pretend as if the 70% was a 90% all a long.

There's also my calculus class where my professor didn't curve or adjust the grading scheme. Of the 30 students in the class, only about 5 passed the class. I'm going to go ahead and brag (because it's unwise to do so irl so the internet's all I got) and say that I got an A while the other 4 who passed the class got a C or less.

The point is, every professor does things differently. Some grade easily, some are tough. Also, some classes are always going to be harder than others. I was a music teacher for several years, and I don't think I could make a music theory class as hard as my calculus class if I tried. Music theory can be challenging, of course, but there's only so many types of questions you can ask. The sheer quantity of material in calculus is larger, creating more of an opportunity to challenge students.