as per the hint it is suppoue to be Vigenere Cipher.
therfore go to : https://www.dcode.fr/vigenere-cipher and decode the encoded string: Uexummq lm Vuycnqjc. Hqjc ie qmud xjas: fycfx{waY5_sp3_Y0yEw_w9vU91}
you will get the following flag:

Welcome to Vigenere. Here is your flag: nactf{yaM5_ar3_Y0mMy_w9jC91}