Go to Apple > About > Storage and tell us how much storage you have and how much is being used. Is your scratch drive on an
extenal external disk?
EDIT: I misspelled "external" and have added the "r".
I have a total of 121gb; 91gb of wich is freely. Honestly I don't really understand the mean of the last question.
You really need a computer with no less than 256GB, but even that is too low.
Is that laptop new enough that you can exchange it for one with ideally 512GB or more storage? (Yes, the price increases the higher the storage gets).
If you purchased it from Apple, I believe they gives you 15 days to return it or exchange it.
If you keep this MacBook Pro, you'll need to offload just about everything to an external drive. I'd recommend a mobile USBC SSD with the highest capacity that you can afford. You'll want to leave it connected at all times and set it as the Scratch Disk.
Honestly I don’t understand. I have friends with the same laptop and the same quantity of GB, and they normally use Photoshop and all the things work well (without USBC SSD). I can't be an exception.
I also don’t understand how possible that the photoshop on my pc takes all the 121GB. I have no other program on my laptop, it’s completely empty, excluding photoshop. I still think that the problem is in the laptop, cause this not normal.
Anyway, thanks for the answers!
"I have a total of 121gb; 91gb of wich is freely."
That sounds very unlikely. A modern operating system and a fairly standard setup of applications, nothing excessive, will usually take up about 70 - 90 GB of your system drive.
With some use, another 20 - 50 GB will accumulate under your user account - user settings, caches, previews etc. All this comes from the various applications installed, from the web browser up.
Photoshop needs a lot of free disk space for temporary working files (scratch disk). This is nothing special for Photoshop, but applies to any pro-level image editor working with pixels. Already you need a bare minimum 250 GB drive to run Photoshop satisfactorily, but that's pushing your luck. For any serious use, a 500 GB drive should be minimum.
Can you post a screenshot from Photoshop > Preferences > Scratch Disks, showing how much disk space is available? Like this:
If you suspect the laptop, run Apple Diagnostics:
How to use Apple Diagnostics on your Mac
You are correct, Photoshop does not require 121GB. Assuming you're running the current version, it requires "4 GB or more of available hard-disk space for installation; additional free space required during installation (cannot install on a volume that uses a case-sensitive file system)".
Photoshop system requirements
What does take up drive space is the Scratch Disk (and it can be a lot):
Set up scratch disks
Since you're running macOS, I highly recommend GrandPerspective. (It is freeware.)
"GrandPerspective is a small utility application for macOS that graphically shows the disk usage within a file system. It can help you to manage your disk, as you can easily spot which files and folders take up the most space. It uses a so-called treemap for visualization. Each file is shown as a rectangle with an area proportional to the file's size. Files in the same folder appear together, but their placement is otherwise arbitrary."
Is there any particular reason that you have not posted a screenshot of your About This Mac > Storage window?
It's important to note that you want to keep at least 10% of your hard drive free - especially your boot drive. In my posted image, the 1st drive and 3rd drive have a good amount of free space while the 2nd and 4th drive do not.
You CAN use Photoshop with that configuration but I strongly suggest that you get an external drive. A Thunderbolt SSD is a great choice and will give you plenty of space.