Can't access MuseScore 4 instruments on MuseScore 4?

My issue is that when trying to use Violincellos as a sound in this one score, it will not let me, yet works in my other score that uses them on MuseScore 4. Checking the mixer on the score that is having this issue, it says the section is using MS Basic, and when I try to change it to violincellos in the Muse Strings, for some reason Muse Strings does not exist. Checking the mixer on the score that DOES work properly, it says violincellos, and Muse Strings exists if I try and change it. I don't know why this is happening, please fix this. I will put both the score that is having this issue (Son of the Tyrant King) and the score that is not (The Angel, violincellos start on Page 16 Measure 80 and work properly).