"Assign working rgb" as default choice when missing color profile

@Pok24012865ecow You COULD assign the ICC profile you THINK is correct but how would you know?

I would tend to open 'leave as is'*, (although it says there that this means "do not colourmanage", that’s not quite right as this will actually now use the Photoshop default colourspace to display the file.)

In your case the working RGB is set to Adobe RGB. 

Next, if the appearance is correct you can ASSIGN the Photoshop default colourspace (now the file will be saved with that assigned profile embedded) and if you require a different colourspace for some reason then - next CONVERT the file to that colourspace.

Why, well some files are not in your default coulursapce and some even have incorrect embedded profiles, so you MIGHT on some occasions see incorrect appearance and thus need to assign a different colourspace profile. 

*of course you COULD assign the working RGB and continue as above from that point. It’s a personal choice to "open as is" in my case.

Assign profile - means

Replace an image file's ICC profile label (the profile "tag") or add a profile tag to an untagged file -

Tagged files: the Assigning of a profile is required very rarely for tagged files and when misused almost always alters appearance negatively, due to a change in interpretation of the image data by the colour management process.

Untagged files: Assigning a suitable ICC profile is necessary, even vital so that a colour managed program can correctly interpret pixel data.

After assigning - the image pixel data is unchanged, but the assigned profile is now used by the colour management process, so appearance may change. 

Convert to profile - means

translate the file's colour information to a new colourspace retaining image appearance*

(*within the limits of the destination gamut). 

The image pixel data is changed, to retain the image appearance whilst shifting it to a different colour space

I hope this helps
neil barstow, colourmanagement net - adobe forum volunteer - co-author: 'getting colour right'
google me "neil barstow colourmanagement" for lots of free articles on colour management
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You shouldn't automatically assign the working RGB - you should assign the profile the file was originally created in. Without proper color management, you obviously don't know what that was, but it's fairly simple to make an educated guess by simply seeing which one looks most correct and natural.

Then you convert to your working RGB if that's the one you want.

A file without a color profile will most likely have been created in an sRGB-type environment, so that's the first to try. If it's from the internet, it's always sRGB.

If it's from a Mac user it will probably be Image P3, since newer Macs have a P3 type display, and it seems to be common practice in the Mac community to use P3 for everything.

Untagged Adobe RGB or ProPhoto are very rarely seen.