A and Å is pronounced differently phonetically and is obviously 2 different letters in the norwegian alphabet.
It is a good question though, the "Aa" is supposed to represent the "Å" sound (which is impossible to describe here, better just googling clips of it) but internationally it just seems to get pronounced as an "A" anyway so he would be better of as Haland. But the "Aa" is also used instead of the Å in norwegian language historically, and quite often in names still. But it is always pronounced as "Å"
It is the same with Martin Ødegaard. In England he is called Odegaard phonetically, but the real prononciation isnt an O but a different sound, and his two "Aa"' is obviously a "Å". Ødegård. Except that the "Å" sound in his name is written "Aa" in Norway as well, which is a more historic way to use it, using the "Å" is a bit more modern.
For those old enough to remember our player from back in the day, Kaare Ingebrigtsen, he was the same. Always written as Kåre Ingebrigtsen in Norway
Not really important though. Languages and names are very hard unless you are familiar with the language. But it is their real name though :)