A few weeks ago I had a problem with the § and < keys being "mixed up in software" on my external Windows keyboard, (the keys are in the right locations physically). I thought the 10.15.2 update resolved it, but now alt+2 on the internal keyboard produces ™ but it should produce @. It used to work fine, problem started some weeks ago, perhaps coinciding with me using the windows keyboard more often... Macbook pro mid 2014 retina, 13 inch.
1 Answer
The Apple input source called Swedish has ™ at Alt 2. Same for Swedish Sami PC.
The one called Swedish Pro has @ at Alt 2.
So make sure the list at system preferences/keyboard/input sources has only Swedish Pro on it.