The supply of Bitcoin being limited absolutely is relevant, and you can buy partial shares of stock (not sure if you can go down to a hundred millionth, but not sure that's relevant). The point is that Gamestop can issue new shares, diluting the existing supply, making it a terrible "store of value". Bitcoin on the other hand has a fixed supply that cannot be increased.

Supply constraints don’t matter when there is virtually infinite availability. There are nearly 19,000,000 coins in circulation and each coin represents 100,000,000 swappable assets. We will reach the heat death of the universe before Bitcoin supply matters.

This is only true if 1 unit is treated the same as 100k units, and it is not.