I am assuming you don't have any data to loose as you have tried Dell SupportAssist OS recovery already.  Your options are to create bootable USB using either of these 2 methods. You can boot from this USB from F12 menu and initiate a clean installation of OS.  Media creation tool (My preferred)  Dell USB recovery tool.  
The heading kind of says it all. I tried BIOS troubleshooting options. I was very unhappy when factory image restore loaded Dell SupportAssist Recovery but it did nothing other than run a loading message. Even when run overnight. What now?
Dell Inspiron 5406 2 in 1 upgraded to Windows 11 now stuck with Bitlocker 
recovery