Closed Bridge several times, rebooted computer twice, fault persisted. Only way was to right click and select open with then click photoshop instead of Lightroom (default) even though Preferences - File Type Preferences - jpg set for Photoshop. Today it's working fine. The right click Lightroom option has disappeared without any updates. Strange.
I've been completely flummoxed by your statement that when opening a JPG, it's been opening in Lightroom instead of PS. The way that Lightroom works is so radically different from (say) PS that it made no sense. I had no way to respond to that.
But I just now interpreted what you said into something that does make sense: There is a plugin to Bridge called Adobe Camera Raw (ACR), which is very much like Lightroom, but Lightroom has a database attached to it, and ACR does not.
If a jpg image has been "touched" by ACR, then you will see a little gridlett in the upper right corner inside Bridge. It looks like this:
If you open up a JPG image that has never been touched by ACR, it will open in Photoshop. However, you CAN open a JPG into ACR. Once that is done, and you just close the image, that image will ALWAYS open in ACR on the way to opening in PS because PS does not understand adjustments made in ACR. In fact, making adjustments in ACR before opening the file into PS is an excellent workflow. The one big catch with it is that if you were to send that file to someone, they would see the JPG as it was before any adjustments were made. To see the adjustments, you have to open the JPG up in ACR first. To avoid this, you have to open the file first in ACR, then in PS, and then resave the file as a new JPG.
I'm going to guess that you've not previously opened this file into ACR. I then have to wonder if a friend sent you this file not knowing the details of the paragraph above.
Anyhow, this JPG file is NOT opening up in Lightroom (or Lightroom Classic), but is doing what it's supposed to be doing — opening up in ACR, and then from there, you can tap the Open button and open it up in PS.
Yes, it takes a bit of mind-bending to wrap your head around this but fear not, it's pretty straightforward once you get past the initial details.