This problem has come up recently. I'm testing the current version of K2ForJ4&5 under Joomla 5.1.0 and Joomla 5.1.1; it may be due to an update. I can't localize the problem more accurately.
Reproduce::
Create K2 article
Go to the Image tab
Click the Browse Server button and select any image
Click Save
Result: I cannot use the image as an illustration for a K2 article.
But if I select an article illustration on my computer, it works without problems.
This problem has come up recently. I'm testing the current version of K2ForJ4&5 under Joomla 5.1.0 and Joomla 5.1.1; it may be due to an update. I can't localize the problem more accurately.
Reproduce::
Result: I cannot use the image as an illustration for a K2 article. But if I select an article illustration on my computer, it works without problems.