It looks like it might be mechanical damage. I'm not sure of that, but it isn't the typical look of a plant suffering root rot.
I water my cacti from the bottom. It might be scary for you to try that, since you've had a bad experience from over watering, but it works well. Just find a watertight container large and deep enough for you to put the potted cactus inside it. Then, fill the container with water, up to the rim of the pot. Let it sit there and soak until you don't see any more air bubbles breaking the surface. At that point, remove the pot and plant from the water and set it aside to drain. Allow it to drain thoroughly, before you return it to its saucer.
This method ensures that the entire root ball becomes moistened. When you water from the top, the water sometimes just runs down around the edges, between the soil and the pot. You see the water coming out the drainage holes, and think the plant has been well-watered, when in fact, the center of the root ball is still bone dry.
Heft the pot in your hand before and after you water the plant. That will help you to learn to determine just when your plant needs water. You'll be able just to pick up the pot and know by the weight whether or not it's time to water yet.
Be sure to use containers with plenty of drainage holes when you repot your Aloe. That will help prevent over watering. In addition, I like to use unglazed clay pots for my cacti ... just the ordinary terra cotta kind. I also use pots that are as broad as they are tall. They are sold under different names, such as
cactus pots or
azalea pots or
bulb pans. The porous clay absorbs excess moisture from the soil and allows air to get into the soil. That's just as important to a plant's roots as water.
It looks like there are 2 separate plants in the container. Is that right? If so, you might want to put each of them in its own pot. If so, then use the same size pot they're in now. If you want to put them both in the same container, choose one just one size larger. In the U.S., we measure the pot across the center of the top to determine its size. We use inches, but I'm sure pots must be measured in centimeters where you live. Measure the pot your cactus is in now, then ask the owner of the shop where you buy the cactus mix to help you choose a pot one size larger. He/she will be familiar with how pots are sized where you live.
By the way, your plant isn't an
Aloe vera, it's an
Aloe maculata.
I'd like to extend a warm welcome to you. It's nice to have you with us here at The Helpful Gardener.
... that is because of overwatering as I didnt know how much water it needed....