Easy answer: use your words! Have you tried having a conversation ahead of time and getting consent, preferably enthusiastic consent? I don’t know your culture well enough to suggest how to open the conversation indirectly in a way that isn’t risky, but it’s worth figuring out. Communication always beats trying to read someone else’s mind.
Homosexuality has only been legal in India since 2018, so the need to hide same-sex attraction is understandably ingrained in older men. Still, I can’t imagine that a man reaches age 75 with no awareness that he is gay. If the men you interact with are hesitant or reluctant, perhaps you’re right about their reasons, or maybe they’re uncomfortable with your approach.
It seems to me that instead of seducing men whose sexual orientation you don’t know, it would be more productive to try one of the gay or gay-friendly dating apps and—when we’re free to travel and mingle again—visiting the LGBT venues in the big cities in India.