Can an average person, of relatively moderate intelligence and barely noticeable innate talent, find decent success in almost any career field as long as they work hard enough at learning what they need to learn and achieving what they need to achieve?

Can most people be achieve financial success if they just pick the "right" field and grind?

Yep.

Money may be needed to attend certain universities/courses/colleges. Sometimes knowing people can help you secure a job or position, however most people graft their ass off in a field.

I would be confident saying that the person you have described will have... Average , moderate , barley noticeable success. Mostly because they lack that drive most successful people have to keep pushing , and are typically happy living with a "safe" income...

Different people are suited to different career paths based on their foundational skills. Anyone who works hard and has a slightly above average IQ can have at least moderate success in any field. However you need proper vision and foresight to achieve the higher levels of a given career.

For example, some people will make decent engineers if they study and learn the formulae and work very hard; but if they can't grasp the abstract and the larger picture of where this component fits into a larger system, they will never be able to innovate and create new solutions, just regurgitate the same solutions that are already available.

It's why so many people who are good in their respective fields get promoted to an upper management role and then fail. They have no concept of how to manage a complexity of systems working together, to see the global picture, to identify talent, or to impart knowledge to others.

No...They are average for a reason. If they climb to the top, they arent average.

I've managed thousands of people over a 25+ year career and most people (average) desire the path of least resistance.

If you start talking about "Grinding" and "working hard" that isnt average people behavior.

Yes it is easy to be successful in the US and much of the world, not rich but successful, if you have average intelligence if you're willing to put in a lot of work. You won't be able to perform to the level of someone with a 130iq who only half asses things unless you put in twice the work or full-ass things.

No.

In some fields, you have to be a very practical thinker or you may have to be like a detective.

For instance, maybe you can learn art or computer graphics, but are you the type of person to come up with creative and catchy images and words for advertising?

If you were given paints how many fine art paintings could you come up with?

If you are a police detective do you have the mind to interrogate and expose criminals?

If you are a psychologist are you mentally quick enough to talk someone out of suicide?

You can't go to school to be "creative" and you can't learn to be a problem solver. You can't learn to be a gifted communicator or have charisma.

In psychology there's something called "Career Counseling" and there's all kinds of psych tests to see what job would be best for you. Not all people can do the same things.