We start with a few hints and a string that we should rearrange. The hints are that this consists of a old school crypto and the string is Us_lnt10ns}1443{FTCDqsysp0srrr4up_t1.
After consulting with my best friend chatgpt, it hinted me that this could be a Spiral-Like cipher. So it goes like this:
The text is 36 chars long and we can create a square shape out of it.
U s _ l n t
1 0 n s } 1
4 4 3 { F T
C D q s y s
p 0 s r r r
4 u p _ t 1
Then we simply transpose it clockwise in a spiral way so that becomes
U s _ l n t
D q s y s 1
C u p _ p 0
T 4 q t 0 n
F r r 1 s s
{ 3 4 4 1 }
And each column contains the flag:
UDCTF{squ4r3_sp1r4ly_tr4nsp0s1t10ns}