Are files scanned for malware during uploads?

NventiveGuy wrote:

I wonder if that code was in a machine-language that an Intel chip

in an iOS device could execute.

The cpu on an iOS devices is not an Intel chip. Code built for an Intel chip will not run, and code built for the Apple Silicon chip on the iOS device must be signed to execute.

You say that iOS doesn’t allow such code-execution?

Correct, executable code must be signed by Apple.

I also was told that files like .doc and .docs may also contain code.

The code you are referring to on .doc and .docx files are Virtual Basic scripts and they don't run on iOS. Even a Word document with a legitimate script is not compatible with iOS and will not work if opened in Word for iOS. Some may consider that a disadvantage in iOS since a Word document containing scripts created on a Windows platform will not display correctly on iOS, but that is the way it is. Apple took the same criticism when they launched the iPhone and it would not run Flash documents on the device and that continues to this day.

I assume that most malicious written for other op-systems can NOT run on iOS.

Correct. Not even legitimate code written for another OS can run.

Also I encountered TIFF files that had malware (in Windows)

Probably true. Other platforms can use third party libraries that may be exploited when used to open the picture file that results in a Buffer Overflow error to break out and execute code. It is actually those libraries that are targeted due to a flaw that allows the code to be executed. With iOS, there is a single Framework created by Apple that is responsible for opening Image files (TIFF, JPG, PNG, etc) called Image I/O.

I come from a Windows background where I used to scan files for Malware by doing a right-click on a filename and requesting a scan. Is there nothing in iOS/iPad OS that can do this?

There is not and for good reason. The whole malware scan process is based on identifiable code signatures to detect Malware and that flawed approach means you are always playing a cat-mouse game to update those signatures to prevent Malware. You will never be able to prevent the next Malware exploit using this approach. The solution is to never allow Malware to execute in the first place. You could certainly place a file with a known Windows Malware/Virus in the Files app, but there is nothing that will allow it to execute or interfere with any operations. Just like you could place an .exe file from Windows in the Files app on iOS, and there is nothing that would allow that to execute either.

The paradigm is a completely different approach. If you are looking for a way to prevent flat tires from nails in the road, you don't need to "scan" the road for nails, you create a solid rubber tire where the nails have no effect on your car. Others may certainly miss a nail that will result in a flat, but it has no effect on you. You may even wonder why are they having to "scan" the road for nails?

Is there an Apple doc that describes this in detail?

There are many documents that describe the Security protections used by iOS/iPad OS.

Apple Platform Security - Apple Support

Some key takeaways specific for iOS/iPad OS.

• The OS is on a Sealed, Read Only partition of the drive where no modifications are possible.
• Apple signs the OS to further protect modifications and uses Secure Boot so it is not possible to even boot from a different partition of the drive.
• Executable code has to be signed by Apple.
• No Remote Login Services are even included. Instead of trying to determine if a remote access client is legitimate, you don't allow them at all. From the above link: "Unnecessary tools, such as remote login services, aren’t included in the system software, and APIs don’t allow apps to escalate their own privileges to modify other apps or iOS, iPadOS, and visionOS."
• Breakout code using memory locations cannot even execute as also seen in the above link: "Further protection is provided by iOS and iPadOS using ARM’s Execute Never (XN) feature, which marks memory pages as nonexecutable."
• Memory locations are randomized using ASLR (Address Space Layout Randomization) where in other platforms you would know where in memory a framework/application will load and be able to modify the memory instead of modifying the actual file. That is not possible on iOS where you not only don't know where it is loaded, you cannot specific a memory location to store any code.
• The advantage of iOS is that Apple owns the Hardware, Software, and Services creating the closed system often referred to as a Walled Garden. While usually this Walled Garden is viewed negatively by others because users are not free to do what they want and there are some compatibility issues, such as the inability to run those Scripts and Flash programs described previously, it is what makes it possible to put those Security protections in place.