The problem

There are big performance issues with versions 1.13 and above of Minecraft.
A lot of lag spikes appear when the game loads and unloads chunks.
Also, when you open the pause menu of the game, a huge lag spike occurs.

Here are some videos of the problem...

A – When loading new chunks

Loading New Chunks Lag Spikes.mp4

B – When loading already generated chunks

Loading Already Generated Chunks Lag Spikes.mp4

C – When you open the pause menu

Pause Menu Lag Spike.mp4

How to reproduce

1. Create or load a world in 1.13 or above
2. Once in play, press Alt + F3 to display the lagometer graph
3. Explore your world and keep an eye on the graph

Also, you can compare the results you get in 1.13 with those you get in 1.12.2. You will see the big difference !