So after a while, support contacted me and made me use a bash script and a software on windows "disk clean up":
Uninstall Sea of Thieves.
Follow this (the support message for deleteing currupted files) :
"I have attached the script, you will need to extract / unzip the folder to gain access to it.
You will be prompted for password when complete, the password is 'Rare' (no quotes). At this point you can either keep the folder as it is, or copy both of the files within it to a new folder of your choosing. -
From here right click the file called: DeleteOldInstalls.BAT and select Run as Administrator. - Select Yes to grant the file access to change permissions on your machine. - Read the disclaimer, we cannot take ownership for any problems encountered. (don't worry I tried it and some people tried it it's safe) - Should you be happy with this type in the bolded text and press Enter: I AGREE - Type in the letter in which drive the game is installed on. It is important the letter is in caps.
Link to download the tool: https://drive.google.com/file/d/1x2WXKSJWFfl80xN-69_Db8BRjAR30YH1/view?usp=sharing. (Safe link)"
Press the Windows button and type 'Disk Clean-up'
From the main 'Disk Clean-up for Windows (C:)' window, ensure Downloaded Program Files, and Temporary Files are enabled and click OK. Then confirm deletion.
The click 'Clean Up System Files'. Once that updates, enable 'Windows Update Clean-up', 'System error memory dump files', 'Temporary Files' and click OK then confirm deletion.
Once Disk Clean-up is completed, ensure the account which owns Sea of Thieves is signed into the Windows Store and Xbox Console Companion app then reinstall the game.
It's easy to do, takes 15 mn (without Sot download time), and the game works just after that. No Directx12 problem of any crash. The game took about 1 mn on splash screen, then a longer loading black screen then usueal, but I guess it depends on your pc but it worked !
Try it, I hope it works for you.