I can squat 150++kg...but still squatting 60 also feels heavy, 100 also feels heavy...hell even standing up from squatting down empty also feels heavy...

No.
Just did speed work with 50kg squats just now. Felt like ... feather.

But I do experience this with bench press. Even 40Kg "feels" heavy.
One thing is... my squat form feels really strong and tight.. but my bench form feels loose and sloppy.

Just so you know 50 kg with the Smith machine doesn't count as 50 kg squat.

Same problem that i working on now.

Squeeze my back; tighten my core; push the bar against my back. It hurts my shoulder but whole setup is solid and tight. No wasted energy trying to balance.

Speed is everything when it comes to squatting. Training with paused squat to improve my explosive movement.

What % are you working on your pause squat and your squat vs bodyweight?

You do low bar? Guess that's y ur shoulder hurt. I do high bar. Feels like all is leg work instead of back.

Freeweigh.

I do 60kg paused rep. Ass to the grass it's like doing business in toilet and explode way up. Reps i keep at 5. Sets i do as much as i could. That is after i finished my main lift - squat.

I do both high bar and low bar depends on what i did for deadlift. High bar is more to quad and low bar more to hamstring & glute.

My 1RM is 125kg and i'm at 60kg BW.

If u feel too much pressure on the back then your form is off. Your ass shoot up too fast.

Squat you gotta keep it consistent. I've been awhile since i hit my 1RM cause my workout not consistent.