Red triangle with exclamation point icon on Table Icon

It appears when something need correcting in the table. Go to Edit fields... and the the offending field or section will be highlighted with a red border.

I have same problem.  Even old databases that were saved and not used in a long time have the same error icon. Editing the table shows no red flags identifying a problem.  Since problem with old databases seems more likely that Ninox has changed something perhaps in a version update

Ninox have indeed updated the software. The red triangle is a warning that you that there is an error in the table structure in some way.

For example - You may have a formula on a trigger on a field or button etc that references another field - if you delete the other field then the flag will show to say that you still have a formula ref that is no pointing to nothing (ie nonscence)