GPU update iMac 2011 for Mojave

Hi, I want to update my iMac 27" mid-2011 (iMac12,2 - i5) to Mojave.

I found the Mojave patch on iFixit but it's written that it doesn't work if you have a video card AMD Radeon HD 6xxx.

I have a AMD Radeon HD 6770M so I guest that it's not possible.

My question :

Is it possible to replace the video card in order to install Mojave (patch) ?

Which video card can I install ?

Thank you very much for your help