By skyforbes The window taskbar was gone first but remaining window remained. I thought if I restart the computer, UI will be restored. But turns out window is not restarting even in safe mode.
Moral of story: Don't always trust LLM
11 Days later: I tried couple of days with no working solutions. Then today, I thought of giving LLM(OpenAI free version) try to solve the problem. I had no hope of repairing OS, and had plan to try new windows installation. But guess what, it worked after some command from the OpenAI. I donot know which command worked, as I had tried some before and it gave me error. But, it worked. After the data is backed up. Time to switch to Linux.
chkdsk C: /f /r /x
may have fixed the problem. The problem may have been related to wsl corruption or what not.
Moral of story: When you have given hope, try every stupid method. You have nothing to lose.