Asked not to is different from forbidden though, no? I’m not a legal expert but I doubt this clause is one they wanted to put in and is probably driven by some legal counsel with an eye on international law.
The school installing software that has terms not allowing those under 13 to use it, because those kids don't have the legal right to consent to the software collecting information from them, has a very real chance of becoming an issue - both for the school and whoever made the decision.
A more direct example would be in Chrome/Firefox/etc automatically checking for updates, which is the equivalent of what Audacity describes in the linked post.
It's not going to happen for all kinds of reasons, but there's a lot that could be said in favour of prohibiting _unsupervised_ Internet access to children 12 and under.
Having children in that age range use the app would require Audacity to seek parental consent by "[making] reasonable efforts (taking into account the available technology and risks inherent in the processing) to verify that the person providing consent holds parental responsibility for the child."1
While they wrote to minors "please do not use the App", they also wrote "The App we provide is not intended for individuals below the age of 13."2 Not being a lawyer, I cannot talk about the implications of these passages.
src1: https://ico.org.uk/for-organisations/guide-to-data-protectio... src2: link in my parent comment