No, you voted at the democratic election. There is no question on the ballot asking whether or not you consent to be ruled by the resulting government.
Differences are astonishing. It's Ok for a despotic country to murder their property, or property of some other country when net effect is positive for them. For them, it's like a plantation: if we cut some trees, or cut grass, then net yield from field will increase, so lets do it. If you are good plant and in good place, you will be left. If not, you will be cut.
For example, it's Ok for Russian Federation to kill their own or foreign people (e.g. British citizens), or start a war just to increase their profit from their natural gas.
Are you positive western democratic republics don't murder and/or start wars for profit ? Last I heard the USA's army and secret services were pretty active.
What's different about their armies and ours ? I mean when was the last time citizens of a democratic republic gave their input on what assassination to carry out or war to wage ?
There is definitely a point about overt, extreme abuse against their own citizens being mostly prevented by representative democracy. But nothing about general consent or agency.
If you don't consent to democracy, you implicitly consent to non-democracy. That means you consent to being ruled without your consent. And that's what you got.
I'm not sure what the parent meant by consent, but you are in fact allowed to leave and resign your citizenship. So you aren't forced into the constitution.
In this case you also have the right to vote and get equal representation. I'm not saying it's an amazing position to be in, but I can't think of any way to make things more consensual on all sides.
In practical sense, voting in a democratic republic is simply choosing, very infrequently, between a set of pre-defined parties. Only the natural supporters of the most popular party are given real agency. Any other viewpoint is discarded by design.
That a candidate is elected, doesn't mean they have anything close to 50% real support in the population. They just need to embody the one set of decisions that the largest homogeneous group of people agree with. That could very easily be a low single digit percentage of the population.
Smaller scope, heterogeneous governments with protected passageways in-between them would be a way to make things more consensual. If people can chose between multiple governments while still staying in similar climate and language-speaking areas, then you could say they really "chose to live in their country".
The agency situation for the average democratic republic citizen is not great right now. Exercising the negative side of consent requires huge sacrifices that many rationally can't make.
Note: I'm not talking about whether Democracy is good or bad, just about my "consent".
edit: fixed typo