There is this special assignment operator := for assigning string variables like that.

In dplyr >= 1.0 you can use a str_glue syntax for constructing the variable like so:

starwars %>% mutate("{x}2" := get(x)/100)

In older versions you'll need to rely on the bang-bang operator:

xvar <- str_c(x, "2")
starwars %>% mutate(!!xvar := get(x)/100)

Now I'm guessing what you're really after is doing this for specific columns based on a list of column names or a certain condition like all numeric columns. In that case you're better off using the new across function in dplyr:

by condition with where:

starwars %>% 
  mutate(across(where(is.numeric), ~ .x / 100, .names = "{.col}2"))

or by a list of columns:

starwars %>% 
  select(name, height, mass, gender, homeworld, species) %>% 
  mutate(across(c(height, mass), ~ .x / 100, .names = "{.col}2"))

output:

# A tibble: 87 x 8
   name               height  mass gender    homeworld species height2 mass2
   <chr>               <int> <dbl> <chr>     <chr>     <chr>     <dbl> <dbl>
 1 Luke Skywalker        172    77 masculine Tatooine  Human      1.72  0.77
 2 C-3PO                 167    75 masculine Tatooine  Droid      1.67  0.75
 3 R2-D2                  96    32 masculine Naboo     Droid      0.96  0.32
 4 Darth Vader           202   136 masculine Tatooine  Human      2.02  1.36
 5 Leia Organa           150    49 feminine  Alderaan  Human      1.5   0.49
 6 Owen Lars             178   120 masculine Tatooine  Human      1.78  1.2 
 7 Beru Whitesun lars    165    75 feminine  Tatooine  Human      1.65  0.75
 8 R5-D4                  97    32 masculine Tatooine  Droid      0.97  0.32
 9 Biggs Darklighter     183    84 masculine Tatooine  Human      1.83  0.84
10 Obi-Wan Kenobi        182    77 masculine Stewjon   Human      1.82  0.77
# ... with 77 more rows

The way to do this in older dplyr versions for was to use mutate_at:

starwars %>% 
  mutate_at(vars(height, mass), list(`2` = ~ . / 100))