I want to make my mod in 1.19.2 and 1.20.1, which to start it in?

I want to make my mod for both versions I play, 1.19.2 and 1.20.1, which one should I start with? It's my first time making a mod, and I'll be using blockbench and Geckolib. I'm wondering if it's better to start in the older version or newer. I'm thinking older but just wanted to ask for more info