British man deported from Sweden despite living there since childhood

I think these are the important paragraphs to note, before this becomes the usual "eh, should have applied in time" topic

Sellers was aware that Brexit might affect his right to stay in the country and, without any communication from government authorities, he considered his best option was to apply for Swedish citizenship.

This he did in September 2021, before the Brexit deadline of 31 December that year.

Not only was his citizenship rejected, but two subsequent attempts to remain in the country under family rights in national migration laws via his partner, now his wife, were also turned down.

So by the time he applied he lived in Sweden already 8-9 years or so. He also likely had a job I assume, would be nice to know the grounds for rejecting his application. There are of course valid reasons to not grant it, but given how terrible of an organisation Migrationsverket is (yes, repeating myself a lot in these posts, I know), I would not immediately assume that the guy did this the wrong way.

I thought it was illegal for states in the EU to separate spouses. It's the reason EU citizens with the settled status in UK ended up with the right to bring their spouses into the UK, for example.

Ok, so he has had 9 years to figure out that he needed a citizenship?

Ok, as a Swede, I will absolutely agree that the government is often terrible at actively informing people about new rules, you have to actively contact the authorities and ask.