Wall-to-wall desk with battens
Given the lengthwise span and the truncated support at the right end, I'd use cleats on the ends and two brackets across the back. 25mm MDF won't handle that load without a lot of bounce and some chance of collapse.
On the left, I'd use four 3/16&quot; x 2-3/4&quot; concrete screws with hex heads. Phillips heads are fine also, but they're difficult to keep from stripping, in my experience.
On the right, two or three such screws.

Across the back, either use screws every 20cm or so, or use two large steel brackets mounted with 3/16&quot; x 1-3/4&quot; concrete screws. Such brackets are unobtrusive to the user and don't catch the eye from across the room. The stability is well worth their use.

If you choose not to use brackets, you may find that you need a stiffener running lengthwise to support the front edge of the desk. It wouldn't need to be at the front edge--it could be back 1/3 or so. An aluminum angle or a tall wooden rail might do well.
Notes about concrete screws
I'm not familiar with what metric screw sizes are available, so I listed fractional sizes. The key is to get at least 30mm of penetration into the masonry.
With concrete screws it's critical to pilot properly. These don't grab like wood screws, where almost anything goes. If your pilot is too small they won't go in or they'll break off. If too large they'll immediately strip.
If you need to remove a screw, drill a new hole. As the threads cut they disintegrate the surrounding material, and a second run-in isn't likely to hold as well.