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.

What you might try is go on Etsy and search for "vinyl storage". Perhaps a small footprint rack like the one below would be a solution.

Archivists recommend storing LP's vertically.  They say that storing horizontally will tend to damage the LP's toward the bottom because of the weight above them.

I’ve played records as long as most any one here and I don’t believe the warpage is the reason Not to store horizontal. I believe @billzame may be right about the bottom records becoming damaged. I’ve sorted through and bought many records that were stored horizontal. The problem with almost every one of them is ring wear on the cover. The ring wear got progressively worse the further down the pile that I went. IF the album had any warp, it was very slight and not problematic.

So 20 albums may not be a problem. Its not the best but if it is all you have, then maybe try it. But an alternative is a closet. I have some of my less desirable in a closet. My son once commented that there were albums behind every door

You need gaps if you sort alphabetically. I did tricks over the years to keep em upright.

I inherited LPs that came with true library shelving with recessed metal tracks and dividers, Expensive, doubtful I would ever have spent that much but it’s the best/easiest system I ever had. My friend had found a library selling it’s shelving.

Actually, I kept only the individual shelves with integral backs/tracks/dividers, and put them on rolling steel shelving, not attractive, but in the garage.