Just another little annoying thing ... using 4.2.9 LTS. Maybe I've missed something?
In the Shader Editor when I create an Image Texture, and click Open to select a file, usually it doesn't display properly because it has been treated as UDIM. So then I remember (usually) to try Open again, click the gear button, and uncheck "Detect UDIMs". I get annoyed having to constantly do this. I think it persists for one Blender session.
An Internet search found one item which comes close:
Go to "Preferences > Keymap > Image > Image Generic > Open Image". In the grayed-out dialog box below the command, uncheck "Detect UDIMs". This works for Open in the Image Editor, but doesn't seem to affect the shader Image Texture.
I couldn't find any other item. Maybe there is another way (I'm not optimistic)?
Oh, that sounds terribly annoying!
I do not know how to make that Setting permanent, if it's possible at all.
This never happened to me, though. Must have something to do with how you name your Images, so in my tests, Name.1001.PNG opens as UDIM, but Name.01001.PNG opens as Single Image. Maybe you can Batch Rename them?
Thanks 
spikeyxxx . OK, I think I have a better explanation. I think I will need to do a lot of renaming.
I have a lot of texture images (used often) which began as captured iPad photos. So many names ended up like MyTexture-brick-IMG_NNNN-01.png. NNNN often starts with 1, so it often triggers UDIM detection.
I further discovered that bricks-1011.jpg opens as single image, bricks_1011.jpg opens as UDIM... So I guess the underscore is a big part of the issue.
I will attempt batch renaming.
Hi techworker1 ,
I tried switching between underscore and hyphen and dot, but they all seemed to trigger the UDIM...I don't know.
Yeah, after bulk renaming and testing again I had to remove the hyphen after the G. Thankfully I have a good bulk rename app (Java, made myself). ;)