My thoughts; I would leave it on Pie.
This N10+ is still running on Pie, the current load will be 2 yo in June still fast and stable.
Security is not an issue unless you do stupid things... no saving dumb bunnies.
The highest I would go is Android 10 and even then you will lose some functionality with trusted 3rd apps like Karma Firewall.
Android 11 and 12 will puke on you. Their scoped storage will waste cpu cycles, reducing usability and functionality especially on an older Android.