Sweden is formally a monarchy but the king/queen has no political power, not even that of asking some leading man (party leader) to form a new government - that belongs to the speaker of the parliament. Essentially the political punch of the regent went down around 1918-20 with full and equal suffrage - the last time a King had seriously tried to impose his will over the government, in 1914, it provoked a constitutional crisis. We might have ended up with a republic but nobody wanted a bloodied revolution - at least few people did and no one who carried much weight - so the monarchy remained and adapted smoothly to the new times. No government today is likely to abolish it.
The constitution as such wasn't changed by the diminishing power of the monarch*: a new constitution came about in 1974 and that one decrees that the King/Queen has no political power, they are essentially a national figurehead, but the real motive for building new was to get a more coherent statement of how the country is really ruled. The old constitution from 1809 (after a disastrous king had been ousted) - inspired by Montesquieu and the idea of separation of powers, like the American one - is arguably still the foundation of political change here and some of it lives on in the new text.
*With typical Swedish smoothness, through the 20th century the designation "His Majesty the King" in laws and order statutes was understood as meaning "the appropriate State authority for this law/this letter". I think this was accepted well before 1914; any Government Secretary or Regional Governor would sign for "His Majesty the King"![]()