It is most likely a hardware failure which will require the Logic Board to be replaced. The Kernel Panic is referencing a GPU or video chip issue:
GPU Panic: [3:0:0][PPLIB] Failed Power Play Initialization.
There is a small chance the problem could be caused by some third party software which is installed which may have come from the backup. It is also possible an externally connected device may have caused the problem.....an external display is most likely, but it could be anything.
Make sure all your third party apps are completely up to date with their latest versions since they may be out of date on the 2014 model since some developers may have stopped support of Big Sur.
Also make sure you are not using any anti-virus apps, cleaning /optimizer apps, or third party security software since they are known to cause all sorts of issues.
FYI, it will not surprise me if it is a hardware issue since the Logic Boards on these 2019 models (especially the 16" model) have a lot of issues in my own personal experience and from numerous posts on these forums. You may have just discovered why the previous owner was selling it.