Who gets to remove a birthright?

The britcard+trust thing is making me wonder how so little fuss was caused by the Home Secretary making Shamima Begum stateless in 2019.
I was shocked that a member of the executive (with the full panoply of due process legal options including incarceration at their disposal) could remove a citizen’s birthright. I mean sure, in a monarchy perhaps the king could strip you of those rights theoretically, just as he might throw you in the tower for treason…
But an elected government tampering with birthright? That makes no sense, and trivialises birthright? If ministers can do this, what else can they do that we haven’t thought of?