8 Elements
There is a guess online saying that there is actually not only the 5 elements we know now , not only Air , Fire , Water, Earth and Ice but also with Sun, Moon and Lightning.
As we know the world of Tangled is connected with Frozen , if the Sundrop flower is the Sun element , well the opposite of sun is moon, and there is a Moon element. Under this logic, the water element should have an opposite too , but what we know now it doesn't . So people make a guess that that is reason why the Nokk was aggressive , it lost its opposite , but Nature has to be balanced so it got aggressive.
The Reason of Elsa Being Locked
Some people think that the reason of Elsa being locked is not because her parents want her to learn to control her powers , but because they are afraid of her being caught . Elsa's power's were known at the age of 8 and Rapunzel was stolen not long after she was born , at that time Agnarr and Iduna would defiantly know that already , so under fear they chose to lock her for her safety.
Olaf
Olaf is made from snow and magic from Elsa , in "Once a upon a Snowman" , Olaf didn't know who was at first , but after he fell of the cliff , the sounds of Elsa & Anna's childhood time when they made him played in his head , and the he finally know who he is . But there is a problem here , Olaf was not alive yet , during Elsa & Anna's childhood , so how does even know that ? Also at the part he told the Northuldra and the Arendelle soldiers about Frozen 1 there are a lot of things that he shouldn't know , but he some how did. So maybe he is made not only from snow but also from memories of Elsa whatever Elsa has gone through , seen , done , he'll be able to know, in other words some people say he is Elsa's "son".
Elsa is Dead
People have thoughts that maybe Elsa is dead. All known , Elsa has become the official fifth spirit , and she has dead once but become alive again. But people notice that other then Bruni all the other spirits aren't really "living creatures" so how about Elsa , could she just be REALLY a spirit but not a human?
Mother Gothel is not dead
Mother Gothel the antagonist of Tangled , in the start of Tangled , it shows that Mother Gothel found a flower under a cliff and became younger with it , think back to Snow white the witch fell of a cliff at the end , but the movie didn't show she died . Hmm... cliff... , so could it be that Mother Gothel fell of the cliff and then found the Sundrop , then became Mother Gothel. Make sense , back to the ending of Tangled , after she fell of the tower , it neither showed her death but she once again vanished , in the Frozen 3 trailer picture , there is a black figure at the right down corner , it could be Gothel , maybe because she needs a new source of magic to stay young , she could be eyeing for a strong source of magic likes Elsa's...
Anna has Powers
People who watch Frozen always have a question : Why doesn't Anna have powers ? People then make guesses : Maybe it would appear in Frozen 3 , maybe she might face the same problem as Elsa did... Maybe her powers aren't visible likes Elsa but instead invisible , her power could be love how she can connect people together , and show love to anyone... Maybe she once had powers but were removed , in Frozen 1 , after Elsa hurt Anna , Pabbie removed all magic on Anna even memories , and maybe he removed Anna's powers unconscious.. well lots of guesses.
This my first time making a post , so if it is not good , you can give opinions , and tell us what you think about these theories