Guys, if I can give you all my piece of advise: do NOT waste your money on writ of mandamus or whatever. You already spent a bunch trying to get the citizenship!
I waited almost 10 months after my interview for a decision to be made (if you scroll a few pages back you'll see my story). It wasn't till I wrote my Senator that my case was unstuck. I was so frustrated also from waiting and waiting, worst experience of my life (and my case was easy). I was even on the local news when my case was finally approved after months of waiting, I can tell you they (USCIS) were quite embarrassed from having held it for so long.
So, write to your Senator, Representative, whoever can intervene and make these people at USCIS do THEIR job!! The lawyers can not do much and I doubt a mandamus is the answer to this problem. They are still riding the COVID wave and blaming it on not enough personal, blah blah blah, it is time to get back to work, make them do their job. Send the Senators, they take it seriously then.