[Mac] my FF14 Stormblood crashes erratically

hello,

TLDR: my version of stormblood crashes my imac: don't know what to do...

I own an IMac and used to play for years (ARR, Heavensward) on windows 7 then 10 on this device via Bootcamp. It worked perfectly.
I made the big mistake to buy Stormblood on mac version. Since the installation process, I constantly and randomly have crashes, game client and operating system. I'm not able to play this game anymore with some kind of good experience.
I created a ticket to the Technical support advised via email do some changes like decreasing the level of details, play in screen mode, lower the resolution, and more surprisingly to update my graphic drivers and some tips in windows 7...

Then the game was awful and continued to crash after lowering the graphical details.

I contacted the support via chat, advised to go to the forum. :confused: I then asked how to get rid of this version and go back to windows version...not possible ask the store
Went to the SQenix store, asked the same question, I was gently advised to ask for technical support. Exchange is not possible as per policy.

Sorry for the long introduction. Now the questions
Did someone experience such a pain using this Stormblood on macos?
How to fix that?

Buying a windows version when I already own a mac one is out of question.

10.12.6, late 2013,
3,4Ghz Core I5
8gb DDR3
GTX 775M 2048Mb

nota bene : my computer never crashes even in high cpu and graphic load when editing and converting large HD videos

Thank you for reading and answers...