In late 2020, Tesla redesigned their 3 & Y Models, mostly in its interior. After the redesign, the accessories that were made for the original center console were no longer compatible with the new redesigned console. That's why, amongst the Tesla community, pre-redesign Model 3/Y are commonly called First Generation/Gen 1 while post-redesign are called Second Generation/Gen 2, making it easier for Tesla owners to confidently shop accessories for their cars.
Tesla Model 3 & Y First Generation/Gen 1 center console is composed by 3 different sections and the drawer has a magnetic non-sliding mechanism.
The Second Generation/Gen 2 models can be identified has the new center console has a sliding mechanism in the drawer.
Why are sometimes second generation model also called 2021 model?
Often times the Gen 2 model is also called '2021' because the Gen 2 was presented to the public in October 2020 and it will start selling in 2021. But an important note Tesla sold in 2021 some Gen 1 cars due to its existing stock so it is wrong to assume that all new Tesla Model 3/Y bought in 2021 are Gen 2. Often times the second gen model is also called '2021' because the Gen 2 was presented to the public in October 2020 with a start selling date on 2021.