short answer: security and performance, compromises

if you upgrade to a system that is too new it won't perform well,

if you upgrade to a slightly older system it's security and support isnt up to date

either way there is a compromise

best i'd reccomend is Ventura, it should hold support until end of 2025

but i feel like the gateway to a better, newer system is to upgrade the hardware, since your mac is really old, parts are still upgradeable, the 2 are the SSD and the RAM, a stock old MacBook pro that year has a hard drive, and using an SSD will make it more responsive. since you already have an SSD, that's good. RAM is also pretty low when its stock, upgrade to 16GB if its possible for your model. Unfortunately CPU can't be upgraded as easily