sunset is what you see at the boundary when you look up - but looking down at the Earth from space -- you will see a boundary in the form of a circle that goes all the way around the world.
If you are standing on Earth at that boundary - you will not see a circle of darkness around your position of light. There is no place on Earth where you can stand and be in the light - and see out at the horizon darkness in a circle around you in all directions.
If you go outside, and you look straight ahead, there is a boundary between light and dark, the horizon. Pretty simple. When the sun is above the boundary, that is the horizon, the sun is up. When the sun sets below that boundary, the sun is down. It's the boundary between light and dark. Has nothing to do with Earth being spherical.
And a circle, is just as it says. It's a circle. There's no mention of a sphere here.
This is an example of how confused Christians have become about the Bible. They think that the "circle of the earth" is evidence that the Bible affirms a spherical planet. As if they don't know what a circle is.
Meanwhile:
13 that it might take the earth by the edges and shake the wicked out of it? 14 The earth takes shape like clay under a seal; its features stand out like those of a garment.
Job 38:13-14
The tree that you saw, which grew great and strong, so that its top reached to heaven and was visible to the end of the whole earth,
Daniel 4:20
Where were you at my laying the foundation of the earth? Tell me, if you possess understanding. Who determined its measurement? Yes, you do know. Or who stretched the measuring line upon it? On what were its bases sunk? Or who laid its cornerstone,
Job 38:4-6
The earth and all its inhabitants are shaking; I steady its columns. Selah
Psalms 75:3
For the pillars of the earth are the LORD's, And he hath set the world upon them.
1 Samuel 2:8
It is he who sits above the *circle* of the earth, and its inhabitants are like grasshoppers; who stretches out the heavens like a curtain, and spreads them like a tent to live in;
Isaiah 40:22
To him who spread out the earth above the waters, for his loyal love endures forever.
Psalms 136:6
Flat earth passages are explicit and detailed.