It's spelled blahaj because I, like most people, don't have an å (yeah, copied that out of the title) on my keyboard. Unless you want us to write blohaj instead, I guess.
Technically you should write it blaahaj instead (if writing Norwegian or Danish, that is). Before the adoption of the Swedish å, aa used to be used in Norway and Denmark for the same sound.
Historically, 'Å' was an 'A' with an additional 'a' on top. This has evolved into becoming the '°'. Similarly, 'Ä' was an 'A' with an 'e' on top, which evolved into becoming two dots.
Interestingly, these umlauts are treated as extra characters in the Nordics but in German they aren't. That's why Swedish dictionaries are sorted from 'A-Ö' while German ones are 'A-Z'. So in order to find German Ärger or Swedish ängen, you need to look at different spots in the dictionary ('Ä' -> 'Ae' (1st letter of the German alphabet) vs. 'Ä' (28th letter of the Swedish alphabet).
I hold down the 'a' key and you can select it on Gboard. But your point stands, I don't expect everyone to make the effort of finding alternate language options.
Also if I’m typing it, I’m referring to the domain name, which I don’t think allows special characters. (Just thinking of registered DNS names allowing all ISO character sets, that would be a scammers paradise.)
domain names can be basically whatever the fuck you want and it kills me how no one in sweden seems to understand this, like come on we're supposed to be good at computers up here, we can do better than just redirecting göteborg.se to goteborg.se..
Generally it's called punycode and is encoded as xn--SOMETHING. Browsers mostly mitigate those scammer paradise tricks by rendering the punycode domain as intended only if it contains characters from a single script. Like if it contains an å, then only other characters from languages that also have å are allowed.