Check with your supplier.  There are more than a few countries in that area of the world that disallow TPMs -- it is entirely conceivable that a system built for that market had the PTT functionality disabled due to local laws.

I have Intel core I3 6006U, I think the system was purchased in UAE (written on the box).

Oddly I just enabled this on my Inspiron 7570 yesterday and the Windows 11 checking tool now passes the check.

To get it to work I had to make sure UEFI & secure boot were both selected and on in the BIOS. Thereafter I could enable PTT. Hope that helps

What CPU do you have, and in what market was the system initially purchased?

Well, my win 10 is running on legacy boot, do I have to do any backups or take any cautions before enabling secure boot and UEFI?

What I am saying is: after I enable secure boot and UEFI will my current win 10 work normally as before?

I called the supplier, and he said: " try to update your bios to the latest version, if the PTT option still there this means that PTT is available on your machine, and for the fact the check box is still grayed out this means there is another option should be enabled/disabled in order to enable PTT, more details will be available on your brand's official site."

I updated my bios week ago, and still the same.

I found an article on Dell about enabling PTT,  it says there is some option(I don't remember it's name)  in the Virtualization section in bios should be disabled in order to enable PTT, but I don't even have that option in the Virtualization section.

That information is not correct;  the option will be there regardless, since the platform supports PTT.

If it's locked out, that's likely been done because of where the system was designed to be sold -- not because of a virtualization setting (which is a completely separate issue from support for PTT).

At any rate, the 6th generation CPUs aren't supported for Windows 11, so if that's your reason for wanting TPM, it's a moot point.

I did not do a complete backup as my machine had within the last couple of days been fully backed up but I would always do so as a precaution. Machine also appears to be working exactly as before.

I have 4 systems that have been cut out of Win 11 because they have a 7th Gen Intel processor.  You might check for yours.  Some of this info may change over the next several months.

Windows Processor Requirements Windows 11 Supported Intel Processors | Microsoft Docs