Categorizing variable and make it a dummy in R

Your sample data does not include a variable called ESG.Kategorien but it does include ESGscore. The following should give you what you want:

Datensatz_final_so$Dummy <- cut(Datensatz_final_so$ESGscore, breaks=c(0, 25, 50, 75, 100), labels=c("poor", "medium", "good", "excellent"))
table(Datensatz_final_so$Dummy)
# 
#      poor    medium      good excellent 
#         4         3        38        32 
levels(Datensatz_final_so$Dummy)
# [1] "poor"      "medium"    "good"      "excellent" 

Note your original categorization places 75 in good AND excellent.

Let's take your data as df:

df<- structure(
  list(
    Company = c(
      "AIR PRODUCTS & CHEMICALS INC",
      ...
      ...
  ),
  row.names = c(NA,-77L),
  class = c("tbl_df",
            "tbl", "data.frame")
)

lets take categories and build a small dataframe, then a bit of dplyr

ESG <- c("poor", "medium", "good", "excellent")
da <- data.frame(ESGColumn = 1:4,FlatESG = ESG)

df <- df |> dplyr::mutate(ESGColumn = floor(ESGscore/25)+1) |>
  dplyr::left_join(da, by="ESGColumn") |>
  dplyr::select(-"ESGColumn")

head(df)

# A tibble: 6 × 5
  Company                       Year gvkey ESGscore FlatESG  
  <chr>                        <dbl> <dbl>    <dbl> <chr>    
1 AIR PRODUCTS & CHEMICALS INC  2011  1209     84.3 excellent
2 AIR PRODUCTS & CHEMICALS INC  2012  1209     81.9 excellent
3 AIR PRODUCTS & CHEMICALS INC  2013  1209     77.4 excellent
4 AIR PRODUCTS & CHEMICALS INC  2014  1209     80.1 excellent
5 AIR PRODUCTS & CHEMICALS INC  2015  1209     78.6 excellent
6 AIR PRODUCTS & CHEMICALS INC  2016  1209     76.4 excellent

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