It’s an Adobe window which says something along the lines of “It looks like you’re using a non-genuine version of an Adobe product”
Has some blurb about why it’s important to use genuine stuff and has a find out more button.
You can’t close it by hitting the x in the corner.
I did wonder whether that pop up was genuine.
I've had exactly the same problem.
I bought a stand-alone version of CS6 from a UK on-line discount retailer several years ago.
The software company supplied me with a download link to Adobe and also an activation code.
I downloaded and installed the software and duly registered and applied the activation code without any problems.
Some time later I suffered a hard drive failure on my PC and had to install all of my software again on a new "C" drive.
Again, no problems with installing and registering the software with Adobe.
Like the OP, I rarely use Photoshop, but about a year ago I started getting these "Non Genuine" messages when I opened the program.
Unfortunately the on-line retailer I bought the software from has now disappeared, so I'm not going to get any help from them.
Since I already installed and registered the program
twice, why wasn't it recognised as non-genuine at the time?
I'm certain that this is just a scam by Adobe to get you to sign up for CC and the only way I can resolve it with Adobe is by paying them money, which I'm reluctant to do.
It's also somewhat worrying to know that Adobe is "looking over your shoulder" every time you use their software.
Because of my very infrequent use of Photoshop, Adobe CC represents extremely poor value for me.
I have resolved the problem by purchasing "Affinity Photo" which for me, does the same things I used PS for, and also seems to be a lot more "user friendly."
Although I was also a Lightroom user, I've also switched to On1 for raw development, so Adobe have now lost me completely as a customer and I no longer use any Adobe products.
With On1 and Affinity I can do everything I used Lightroom and Photoshop for, and don't have to pay a monthly rental fee.
In fact, with layers and masks, On1 alone does most of what I needed LR
and Photoshop for.