I am experiencing the same issues. I've tried it on two client sites after another client reported the issue on their site with the same result. I also tried it on this demo site: https://demo.circle-interactive.co.uk. These are 5.24.x sites. Since two people reported they were able to generate new dashlets using 5.25.0, I updated one of the sites to see if this would solve the issue. It did not.
- Choose a report that does not have a dashlet already. Contribution Report - Top Donors.
- On the Top Donors >> Access tab, I enable Add to My Reports and Available for Dashboard and Refresh Results.
- Under Reports >> My Reports, Top Donor is not shown. Nor is it shown as a dashlet when I view Configure Your Dashboard.
What I did discover, is that the values for Add to My Reports, Available for Dashboard, Limit Dashboard Results and Cache dashlet for are not being saved. (I've tried this in two browsers: Chrome and Firefox updated to the latest versions.)
- Load a report and view the Access tab.
- Update values for Add to My Reports, Available for Dashboard, Limit Dashboard Results and Cache dashlet for fields and click Refresh Results/View Results.
- Return to the Access tab for the same report and verify that the values are what you set in step 2.
- Load a different Civi page (such as Reoprt Listing)
- Return to the Access tab for the report where you set you new values. In my case they have reverted to my original values. And no dashlet/no my reports.
What's also strange is that I thought that using the browser's Developer Tool reload option Empty Cache and Hard Reload would revert the values; but it did not. It seems that this only happens when I load a new Civi page and then return to the Access tab of the report.