If you're not aware, Windows 11 has CPU and TPM requirements that this system is far too old to support.  It must have been installed by bypassing the CPU check. Bottom line:  this model dates from 2012.  Even if it has a TPM, it will not be recent enough to support Windows 11 -- and the CPU in it is likewise unsupported. Microsoft has publicly stated that it may update Windows 11 to enforce those requirements -- the appearance of the error you're seeing, if recent, may just be the opening act in that play.  
After a little stroll on Google I noticed a caution icon on my Windows Security icon on the task bar. I opened it up and it read.                     Device Security  There is no TPM available. Please check your BIOS settings.  A google search on how to check my BIOS settings was not helpful. I can't even find if this computer is supposed to have TPM.  This computer is running Windows 11.   It's the first time I've seen this caution. Thanks for any thoughts, Rick
There is no TPM available