Merde

Vvr ktdk vl jvtzsyHBI{fnzcievs}

From the description, I understand that it is Vigenere Cipher with key. The key is confidentiel.

I used this decoder (https://www.dcode.fr/vigenere-cipher) with the above key and I get the flag.

Merda

ymj kqfl nx gwncjqHYK{uneefsfutqn}

From the description, I understand that it is Caesar Cipher. I used this website: https://www.boxentriq.com/code-breaking/caesar-cipher with the autosolve option and the flag appears when the key is 5.

Thanks for reading!