Replacement has 6 rows, data has 2

what is wrong with my code

d <-
tibble(group = rep(c("normal","covid1","covid2",
                     "covid3", "covid4"), each = n)) %>%
mutate(treatment = rep(c(0,1,2,3,4), each=n),
       y = c( group=="normal" ~(rnorm(n, mean = mu_n, sd =1)),
       group=="covid1" ~(rnorm(n, mean = mu_c1, sd =1)),
       group=="covid2" ~(rnorm(n, mean = mu_c2, sd =1)),
       group=="covid3" ~(rnorm(n, mean = mu_c3, sd =1)),
       group=="covid4" ~(rnorm(n, mean = mu_c4, sd =1))))

I got an error
I want to settle the value of y to be rnorm distribution with different means depending on the group

Error in `$<`(`*tmp*`, "call_text", value = c("... %>% ...", : 
replacement has 6 rows, data has 2

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Thanks for letting me know.
Sorry if I cause any disturbance.