Overdubs
Traditionally things like vocals and lead guitars are recorded by themselves after the bed tracks in a process referred to as “Overdubs”. The reason why these particular elements are recorded on their own is that you want to capture these sounds in as discreet a manner as possible. In other words you don’t want any other sounds leaking into the microphone, this is especially true when recording a lead vocal. If you have a single room setup hopefully you have a closet nearby.