I copied executable files which were labeled as executable in the file manager when single-clicking it (example: usbview, lshw-gtk in /usr/bin) from computer to usb then I was able to execute them even when executable permission was disabled.

I tried executing other file extensions as per the list: https://askubuntu.com/a/174356
But, I wasn't able to execute shared libraries like nethogs (no extension), file extensions .so (runtime object), .a (static library), .elf (executable files not object code files) when executable permission was disabled.

While executing some .o files through the terminal but I got error "cannot execute binary file: Exec format error".

File extensions .exe requires wine executable, .tar requires tar and make shared library (run without ./ as prefix), .deb requires dpkg shared library (run without ./ as prefix). Extension .ko I haven't tried as it is related to drivers and kernel modules.

Basically, as rknichols said execute permission is required when directly executing it. If a file (script/source code, static library, shared library, .bin, .elf, or .so file) can be executed via ./[filename] it can also be executed through the GUI when executable permission is enabled.

A .bin can be an executable file (Unix Executable File) or something like a binary disc image etc. Source: https://fileinfo.com/extension/bin

For differentiating between a binary file and binary executable file (or binaries), would you say that if a file is directly executable via command line or GUI then it is a binary executable file else if the binary file requires another program to run it then it is just a binary file? (Example: .jpg is a binary file which requires an image viewer to read/edit it)

I still do not understand what is the goal of this thread.
About binary files: https://en.wikipedia.org/wiki/Binary_file
About text files: https://en.wikipedia.org/wiki/Text_file

About executable:
1. you can set or reset the execute flag on [almost] any file. If it was set the system may try to run it, if it was unset the system simply refuses to run/execute it (= even will not try to do anything).
2. a file can be runnable if the system is able to run it. It should have a special format which can be handled by the kernel. These files are usually binaries.
3. a file [or dir] itself is not runnable, but there is an associated executable which can handle the given file. In such cases execute means: run that associated app (belongs to point 2) [instead of the file] and pass the file as an argument to the app. Usually scripts, images, videos, documents (among others) work that way.
4. additionally there are shared objects (like .so files) which are not standalone executables, but real executables or other so files can run the code.

In unix/linux the extension is more or less irrelevant, the system does not care about it at all (but it was already mentioned).

Did you read my post explaining about the file manager?
What you are asking is to prevent the file manager from executing certain things. Which file manager are you using, what behavior are you really looking for -- why are you asking ths?

The topic shifted towards file executing/executables and permissions from the posts #7, #8 and #9.

From my point of view, I am trying to know whether executable permission in Linux is useful for adding an extra layer of security for USB devices apart from features such as disabling autorun, automount, autothumbnailing, USBKill etc.

And this is from the point of view as a Linux user (what the Linux user can control) not from attackers point of view who may use technologies like Bad USB, USB Rubber Ducky etc. As a Linux user, if I give a removable drive to someone to give me some data or just connect a USB device to my computer which I feel may not be safe then I am taking reasonable security measures to prevent viruses from the USB device.

I am just using the GUI file manager (Thunar File Manager) to right-click open via terminal emulator for .sh scripts and right-click execute for executables. I have not associated scripts with other programs and then used the file manager to open them. I have run all the files via the terminal emulator by the syntax ./[filename] for checking the executable permission. I have used the file manager as a way to double-check only for .sh scripts and executables. I understand that if I associate a script/file with another program and use the file manager to open it then I am not executing the script/file on the usb rather I am executing that associated program to process the script/file on the usb.

Correction, I am not able to execute "files labeled as executable in the file manager which do not have any extension" when executable permission is disabled. (Extremely sorry)

And it is not just about security, personally speaking the discussion on file extensions is helpful to me as it describes how the files are handled/executed by Linux. Thank you for the contributions