Don't be fooled unsquaring your frame...

So after trying to adjust my frame to the bed I had to rise my front right corner insane 4mm up. Which caused stress on the back side of that extrusion and definitely things became not parallel.. although mesh improved from 0.7 to 0.255.

But I didn't like that I had to rise a corner by 4 mm because I knew I assembled it straight and flat..

So I began to tear things apart. And like I thought after remeasuring everything my frame was kinda perfect ( leveled top and all posts straight)

So I decided to measure the bed corners by putting it on a flat stone. ( I rotated it few times to make sure readings repeat on all references of stone to the bed) and here what I got.

My bed indeed had a sagging corner by more than 1 mm. And all I did with that youtube technique (which is good) is bending my extrusions so they fit the curved bed.

Just make sure to check your bed before you spend hours on your frame..

I will try to bend the bed and will update with mesh results. Cheers