I recovered some junked DLINK DIR 615 I1s a while back. These routers were soft bricked (on-and-off remote access). A peek online hinted at a built-in recovery/safe mode.

That failed in modern browsers. The suggestions here didn’t work either. Why? Who knows? They were made in 2012 and discontinued 2017. Using the “recreate the developer’s environment” trick, a 2012 browser (Opera) revived the custom firmware updater! Now they work again. The end.

Default firmware: https://tsd.dlink.com.tw/