When to offer a draw?

I wonder when it is a good moment to offer a draw in chess?

I'm aware that draw can be due to various reasons when it is decided that it's a draw, e.g. stalemate, insufficient material, move repetition.

Recently I played a game where the opponent offered me a draw while being in a losing position. Actually it was a mate in 5.

I got offered a draw.

I didn't have a choice but to decline.

In The Queen's Gambit... I think it was in a last episode when Borgov offered Harmon a draw with no counter play opportunities for himself. As Magnus explained in one of his videos on Youtube, it was indecent and actually even insulting offer

And I wonder now... are there any unwritten rules, agreements or fair play principles that state when it is OK to offer a draw and when it is NOT OK?

I'd say don't offer a draw that you wouldn't consider if you were sitting in your opponents seat. If I see the position closing down with very minimal activity available for each side, I'd offer a draw because I'm fine with the half point but am interested in seeing if my opponent feels the same. In OTB tournaments, I'd offer an early draw if all I need is a half point. Regardless of the event or situation, one thing that I try to do is allow a significant amount of moves to pass before offering a new draw offer.