I have this reasource pack i really like and it has a clear ui i want to know if it is against speedrunning rules

According to the rules: "Features that are banned include but are not limited to UHC Ores, transparent inventory UIs (and making things more transparent in general), and brightened Endermen." TLDR: no

If it wasn't clear WHY it isnt allowed, it gives an advantage to the player.

No, it is not allowed because it gives a competitive advantage. Its like fog vs no fog no fog isnt allowed cause u cant turn it off in vanilla and it gives a competitive advantage clear UI is basically turning off fog but in the UI