Let’s try hex atbash. So your index is:

0123456789abcdef
fedcba9876543210

Notice how “f” seems to be used as a split ? Reverse the string to see it better

4bf4df55f35f39f50f52f4ff47f52f45f53f53f35f39f33f42f4bf

Make groups of 3

4bf 4df 55f 35f 39f 50f 52f 4ff 47f 52f 45f 53f 53f 35f 39f 33f 42f 4bf

Remove the trailing F of each triplets

4b 4d 55 35 39 50 52 4f 47 52 45 53 53 35 39 33 42 4b

Convert Hex to Ascii

KMU59PROGRESS593BK

After playing with it a bit I noticed something when reversing the string

u1010eiviiipr35qu35usiviitwjo

See the keyword presquevu in there ? It’s a mix of roman numeral and leet speach

u 10 10 ei viii pr35qu35u si vii tw jo

uxx88presquevu672jo

Rot +2 will give you

rob75i466dk