Is it ok to stack LPs horizontally?

OP has 'run out of storage space'.

So why does piling records horizontally occupy less space than vertically?  The records have a fixed volume.

And yes, horizontally will cause warping after a while.  Gravity will act on the less well supported outer areas and cause them to fall.

LPs should not be so loosely stacked that they lean to one side, weighing against each other.  Nor should they be tight enough to create side pressure.  Just densely enough so that the stand vertically without pressuring each other.

@heretobuy      Goodness, that rig looks highly unstable on its tiny angled feet.  Anyone who has lifted that number of LPs knows how heavy they are.

A dog or a small child could accidentally knock it over and the falling LPs cause injury or worse.  I wouldn't have it in my house.