R6120 wifi is not working.

Is it only wifi that doesn't work ?

What firmware version are you on? 

I usually don't recommend the genie. I usually recommend people use the device through the browser. 

what modem is it connected to?

> [...] Today wifi doesn't work. [...]

   "doesn't work" is not a useful problem description.  It does not say
what you did.  It does not say what happened when you did it.  As usual,
showing actual actions (commands) with their actual results (error
messages, LED indicators, ...) can be more helpful than vague
descriptions or interpretations.

   Visit http://netgear.com/support , put in your model number, and
look for Documentation.  Get the User Manual (at least).  Read.  Look
for the LED descriptions and "Troubleshoot".  Further reading might not
hurt, either.

> [...] Tried updating the firmware [...]

   "Tried" _how_, exactly?  From which version to which version?

> [...] and it appears NetGenie doesn't support this model any more.
> [...]

   "appears"?  "NetGenie"?  This, or something else (what?)?:

      https://en.wikipedia.org/wiki/NetGenie

> [...] I downloaded the latest firmware manually and I get a message
> it's a corrupted file when I try to unzip it. [...]

   "try" _how_, exactly?  What, exactly, did you download?  What,
exactly, did you do with what you downloaded?  What's the actual
message which you got when you did what, exactly?

   None of this is a useful problem description.  See "not a useful
problem description [...]", above.

   Possibly relevant:

      https://community.netgear.com/t5/x/x/m-p/1721037#M124018

   Visit http://netgear.com/support , put in your model number, and look
for Downloads.  (For older versions, under Firmware and Software
Downloads, look for "View Previous Versions".)  Find the kit(s).
Download the kit(s) you want.  Read the "Release Notes" file for
instructions.  (In the User Manual, look for "firmware", and,
especially, for a topic like "Manually Upload Firmware to the Router".)
When that fails because of a deficient User Manual, try:

      https://kb.netgear.com/23960
      https://kb.netgear.com/31573

> [...] Is my R6120 just too old/obsolete to still work?

   No.  It never was a high-performance model, but it should work about
as well now as it ever did.