Hi @Dama Gab,
Sorry to hear about the trouble you are facing. I agree with @Jacob Bugge; this generally happens when the third-party application is interfering with Illustrator. In that case, you may try running the app in Safe Mode (Mac/ Windows) and launch Illustrator only. Then, open/ create a new document, try the shortcuts, and see if that works. In Safe Mode, your system starts to perform certain checks and prevent third-party software/ services from automatically loading or opening. If it works fine in Safe Mode, then open other apps one by one, which you usually open, and see which app is conflicting with Illustrator. You can check and find the culprit app/ process/ plugin/ extension with the help of Activity Monitor/ Task Manager, and then you'll have to close/ disable/ uninstall them on your user account and then restart Mac/ Windows machine in normal mode.
Also, it can happen due to corrupt preferences. In that case, you may try resetting them.
I hope it helps!
Regards,
Anshul Saini