F-1 Student to Green Card: YES - It is Possible
F-1 international students can be sponsored for green cards. This works easiest for people not born in India or China but all nationalities can be sponsored for green cards from F-1 status.
If someone is telling you it is not possible to be sponsored for a green card from F-1 status, it is absolute nonsense. Sorry.
A company can have a POLICY of not sponsoring someone for a green card, but a policy is not the law.
The law permits PERM sponsorship for F-1 students.
Anyone who says otherwise should produce a law or regulation or policy memo to elaborate their position. Ask for a formal legal opinion so you can sue them for malpractice.
It is just 100% nonsense that you have to be in a dual intent non-immigrant visa status to be sponsored for a green card.