I think preferably, I never notarized mine in any application, everything went just fine. I hear a lot of people saying its required so it might be better. I think its just helpful.
What I did was list all the financial documents included, write a statement that went something like "We will be fully responsible for Mohamed's studies, accommodation and allowance", I just made both my parents sign it at the very bottom and that's about it. This was back in 2019.
Did the same letter about 4 months ago to renew my visa and didn't have it notarized either, everything went smooth as well.
The only thing that I notarized were papers that had to be translated into English.
My birth certificate and house ownership papers were both issued in Arabic, so I had them translated and stamped by the government of Dubai.
Hope that's helpful.