Here is a dplyr solution using an ifelse statement:
library(dplyr)
df %>%
mutate(C = ifelse(B >= 6, A+1, A))
A B C
<dbl> <dbl> <dbl>
1 2022 2 2022
2 2025 7 2026
3 2030 8 2031
df <- structure(list(A = c(2022, 2025, 2030), B = c(2, 7, 8)), class = c("tbl_df",
"tbl", "data.frame"), row.names = c(NA, -3L))