Yep! According to singer Alex Porat, some musicians hear what’s known as a “click track,” which is sometimes overlain on their song ― and sometimes heard as-is.
The singer stitched a TikTok video that said “POV: you’re listening to Taylor’s in-ear monitor during Cruel Summer,” wherein a countdown and a loud clicking sound drowned out most of the music.
Alex said that when her friend asked if this was really what singers hear on stage, she replied, “Yes, it is.” More here.
I guess that makes sense because everything needs to be so tight when performed live. I do wonder, however, how bands managed before these earpieces were available and how they, for example the man above and his band, kept things together so well.
Sometimes the click track is so you can have sequenced tracks playing along too. We did this in a band I was in where I needed other keyboard tracks I couldn’t play live in addition to the guitar part I was playing. This click only went to the drummer to keep us all in sync over a monitor speaker - no earpiece.