Hello Grigore,
I have here some dummy questions (forgive me for my ignorance), but I need to ask them just for the sake of curiosity (maybe, after all, we can get somewhere if I articulate questions in the right direction/right format for this problem):
> If I put a proprietary AMI BIOS, GRUB2 works without issue in gfxterm mode and boots Linux without issue.
[1] What Linux architecture are you using (32 or 64)?
[2] Which Linux distro?
[3] Which kernel version?
If you put AMI BIOS, the following questions I would like to know:
[4] Are you using 32 or 64 BIOS?
[5] Which mode are you using for booting (legacy/CSM ON or UEFI/CSM OFF)?
[6] In the accordance with [5], what video component you have set with CMOS: vBIOS or GOP driver?
Not sure, but it seems to me that you are using too old/outdated GRUB2 version (or maybe I am also mistaken)?
[7] Could you tell us, which GRUB2 version you are using?
Thank you,
Zoran