Why is Minecraft so ugly?

I have the normal 1.8.8 version without Labymod or anything. Graphics settings are all very high.

Get shader & texture pack and Minecraft is no longer ugly

If I see it correctly, that's the Sphax resource pack.

What is ugly about it? Just download another resource pack?

It looks like always. One must not forget that Minecraft has never relied on graphics, especially since it is now over 10 years old.

Have you ever tried another resolution? Looks to me like a 4: 3 picture was drawn to 16: 9. The FOV shouldn't be too blatant.
Maybe. Also switch on VSync, at least the buggy or white edges should go away.

The game is just a few years old, back then PCs weren't much more.

But there are texture packs and shaders that can be installed. I think that's quite good: https://soartex.net/downloads/
There are for different launcher and versions.