Adjustment layer mask not displaying on image

[RG631971]

Okay, running Photoshop 24.2.0 on 64 bit Windows 10 10.19045.2604.

Very simple circumstance that seems to have changed.  I open an image and apply an adjustment layers, curves in the attached example with an associated mask.  Subsequently, Apply Image from the Image menu to the mask with the Layer Merged and Blending set to Multiply.  Previously, and per many examples, tutorials, etc. the image displayed changed to grayscale like image.  Last night, this quit happening which makes adjustments and use of some long standing techniques much more difficult.  This is really aggrevating since I can not figure out what caused the change.  Anticipate I inadvertently did something but have not been able to figure out what.  Any help or explanation would be greatly appreciated.

[S_Gans]

Hi. Had you tried this with a Curves adjustment before? While Apply Image will create a grayscale image IN your mask, it doesn't make your image a grayscale. Masks are about blacks, whites and grays - color doesn't exist in a mask, because it's only about whether that layer displays or hides your adjustment. So, if you're using an adjustment layer that's made to alter color settings, it won't grayscale the image out at all. Now, if you use that same masking technique on an adjustment layer meant to remove saturation (eg: Black and White, Hue Saturation, and others), you can control how MUCH of that happens. 

The sole purpose of a mask on an adjustment layer is to show and hide how much of any adjustment layer affects the image below.

[RG631971]

Thanks for your reply.  Yes, I had tried this with a curves adjustment before.  For context, this is directly from a video lesson on the Udemy platform but I have seen it other places as well.  I understand the concept of blacks, whites, in masks and love the flexibility the "grays" can provide.  However, (just to be clear) the sequence is create the curves adjustment layer with mask though others could be used I think.  Then add the "Apply Image" from the Image menu.  After this process, the effect was described as a lumnosity mask in which the curves adjustment (Ctrl M) on mask could be used to emphasize highlights, shadows, etc.  Indeed this is what it now does on the mask thumbnail.  However, the main image is still in color and remains unchanged.  The process is reminiscent of the "texture" layer in frequency separation.  Just to be sure went back an double checked as I wrote this reply.  Not leaving anything out and would be happy to provide specific context for reference if you think that would help.  Just baffled at this point.  Have watched the video segment numerous times anticipating I am missing something but to no avail.  Again, appreciate any additional insights you may have.

[RG631971]

Found the answer and it was ridiculously simple.  Alt clicking the mask thumbnails "transfers" the thumbnail image to the main image where it is easier to see any adjustments.  Just for context, I have been really focusing on Photoshop capabilities of late and never remember anyone mentioning this or doing it previously.  Also, finally stumbled across a website covering the topic that I would be glad to provide if interested and permitted herein.  Also, wanted to say thanks for the prompt response to my post.  Your description was valuable in that it represents a concise description of what is actually happening.  Such info should really help folk's understanding.