I am testing some of my datapacks when i noticed a lot more lag as soon as i loaded into 1.21.4. So i created a new world without them to investigate.

Symptom 1: World Creation takes a long time, causing system stutters, 3x more so, if not more, than in 1.21.3.
Symptom 2: System stutters after loading in, as the world renders, again 3x more, if not worse, than in 1.21.3
Symptom 3: System stuttered for half a second when loading a single pre-saved hotbar, to which there was no lag from doing so in 1.21.3.
EDIT: Symptom 4: After further testing, where in 1.21.3 my framerate was consistently at or above 60 FPS(where i limit), now my frames consistently drop to around 40 FPS every few seconds.

It is my conclusion that this amount of lag is not normal, and i myself cannot explain it. I made sure to check that nothing on my system was causing it, and kept my enviornment the same for testing both 1.21.3 and 1.21.4.

Symptom 5: I am now experiencing lag on the menu panorama, after sitting on it typing for about a minute. I am unsure what to make of this.

I checked my CPU & GPU, both are extremely under stressed, sitting below 10% utilization.
My ram usage seems to be normal, but that i cannot tell without further testing, and i have a family event i am late for. I will add more info as i am able to find it.