Hello
my fairphone is stuck with that message
can’t load Android system. Your data may be corrupt. If you continue to get this message, you may nneed to perform a factory data reset and erase all user data stored on this device
Is there another way to recover without losing datas ?
I guess it happend while you did an update. Usually you can choose retry and after 5 retries or so then it should boot back to the old slot.
Did you try that? (just don’t choose format data)
if you remember living on the edge of available space, freeing some up will make it boot again
I don’t remember a recent update.
I tried several times already 
Yes I had a message about not enough space but I can’t empty because it shut off before I can delete files
The topic linked to above shows a way how it may be possible, but it’s not exactly novice user entry level territory, and success may vary …
If you can’t get this way to work somehow, most probably you will have to do a factory reset, wiping your data.
So, it’s worth to read through what @tcecyk is talking about there and then maybe ask questions on details you need help with.