In the past I simply used the miniHud overlay to see the border of the world's spawn chunks. And in most of my previous worlds I spawned close to 0,0 plus since the "always active" world spawn area is quite large I wasn't worried that miniHud might take a while to give support for 1.19.
So, just for the fun of it I created a new world for 1.19... and it spawned me around (-300, -300) and forced me to use my head. Used a boat to get to (0,0) in the middle of the ocean and built a small platform there. Then I suicided, and surprise... I respawned in the island at the aprox -300,-300 spot.
Now I am in a bit of a dilemma... which of the spots (0,0) or (-300,-300) is my default world spawn? And most importantly... the center of the always active world spawn area? (single player)
And if I place a bed, will that reset my world spawn - together with the ALWAYS ACTIVE CHUNKS to be centered around that spot?
World spawn is where you respawn if you die without a spawn point (e.g. bed), so it is at -300, -300; the exact location can be found with a compass (the player randomly spawns within a 21x21 block area centered on the exact world spawn point; this means that in your case it could be anywhere within a 3x3 chunk area centered on chunk -19, -19), and it never changes unless you use the /setworldspawn command. Note that spawn chunks are based on chunks, not blocks (F3 shows the chunk coordinates, or block coordinates divided by 16 and rounded down; -300 / 16 = -19), and is 19x19 chunks, or 9 chunks in each direction (for the fully active area, excluding anything that depends on a player being nearby, including most mob spawning and random block updates).