Handling Lower Rated Opponents

there are lots of such lower rated players who play such openings for drawing against higher rated opponents.

This is one of the example my opponent played vienna game and even after following all book moves and not doing any mistakes at the 19 move It was easily drawable for a lower rated player so I took a risk by playing 19.g6 which is a mistake but only by that move I won the game.

These days many lower rated players play openings like Vienna game, Bishops Opening, Four Knights Game Some Lines In scotch. in these openings if a experienced lower rated decides to have a draw he can force it against higher rated.

Magnus abandoned the 2900 mission because of this reason.

What should we do against such lower rated players?

Lower-rated players often play for exchanges and simplifications to reach equal, drawish positions. Try to avoid unnecessary trades. Keep pieces on the board, particularly queens, to retain complexity and create winning chances later in the game.

Correct

but in specific openings there the drawish exchanging line is forced

In some lines a skilled player, especially if they have white, can reasonably push for a draw against a higher rated player. Seems like two ways to avoid this as black are to play sub-optimal lines or to play openings with less drawing chances (e.g., Sicilian).

At my level, though, this isn't a problem!

what are sub obtimal

Moves that are not the best. In this case, playing a less good or dubious move in order to reduce the chances of a draw. Your 19 ... g6, for example.