Broadly speaking, manual labor is producing a physical good or service. A plumber cannot write an algorithm to fix clogged pipes and sell it to desperate homeowners. Manual labor varies widely in skill-level. Non-manual labor, on the other hand, is the act of creating information such as software or digital art.
Programming is the process of designing a protocol and having machines (computers, robots, CNC, vehicles, etc) preform it. Software architecture (hopefully) keeps the code human-readable and avoids spaghetti. Art and writing are also information jobs. Such work is useful outside of "art": there is graphic design behind a slide show and wordsmithing behind a business whitepaper. The overlap of writing and coding is partly why Python, C++, etc are called programming languages.
After decades of rapid growth, software development jobs seem to be in decline. Tech layoffs are in the news and there is a predicted 10% drop of these jobs in the next decade. (I think) art/writing jobs have also proportionally declined as a whole.
The "obvious" explanation for this decline is that software did it's job: after decades computerizing our world we largely succeeded and now there is less demand. Similarly, improvements in tools such as Powerpoint an NLP AI's such as Grammerly have reduced the need for human editors.
On the other hand, many occupations are still manual. Home caretaker jobs, driving, electrician work, cooking, waiter-ing, and cleaning are just some of the many, many occupations which have resisted automation. Machines have made manufacturing work more efficient by reducing the total man-hour cost. But proportionately speaking, most of the man-hours keeping our factories going are spent on tending to the machines, driving, and other manual labor tasks.
The "standard" picture of technology is that manual labor gets replaced by "information labor" as we automate the world. But are we actually in a time-period (at least in the short term) where the "information world" got "ahead" of the physical world (robotics, self driving freight, etc) and will not need a big labor pool?