Hi there, good to see somebody running a 11 year old MBP.
I have the 2011 model which works flawlessly with 16GB and a 1TB SSD.
However, the 2010 does not. I have tested this back in the days with an i7 version a friend brought over to increase RAM. Regardless of the many people out there who show screenshots that seem to support their claims. It boots, but it will not work for long. If I remember correctly (it's really been a while

), the problem starts as soon as the OS tries to access the additional ram address space but I am not 100% sure whether 12GB will work. I know it did in my previous 17" but that model had the silver keys instead of the black and I think it was older than 2009 but I can't be sure anymore. Having said that it would seem feasible that 12GB therefore could work in your model. But frankly, what is it you're trying to achieve?
Having 12GB instead of 8GB will most likely come with a performance hit (8GB and 4GB) due to the way the MBP used to manage memory in those models. (There's a reason Apple only recommends 8GB max). If you are in need of more RAM then you probably will hit another HW barrier anyway in other areas and buying a newer MBP (maybe even a 17" if that is why you're still using yours) seems more sensible but that's just me.
You're stuck with a laptop that has "slow everything" built in from SATA to graphics to low res screen. Any money spent on it seems wasteful to me and I am the first to admit that my 2011 17" is still running fine although I am using a 2016 MBP for work. Overall there is just nothing useful in those old machines that would make me want to invest money to keep them going. The next thing that will die is the battery or the GPU and then you're hard pressed finding a replacement for it.
Each to their own. To sum it up, 16GB will not work. It will cause you more trouble than you ever wished for. 12GB may work because it did so in my older MBP but I have no real evidence of that for your particular model.