separate_longer_delim()

tibble(x = c("a,b,c", "d,e", "f")) |> 
  separate_longer_delim(x, delim = ",")

## # A tibble: 6 × 1
##   x    
##   <chr>
## 1 a    
## 2 b    
## 3 c    
## 4 d    
## 5 e    
## 6 f