Hi!
It is, indeed, possible to set up automated passing of tiles that can't be called.
This setting is in the player preferences, which can be seen by scrolling down beneath the playing area of a game (on desktop) or by clicking the 'burger' menu in the top right during a game (on mobile).
You can also use this preference to auto-pass chii, pon and kan calls (similar to other online mahjong platforms).
Some caveats with the automated passing:
- There is a chance that using automated passing will allow opponents to infer information about your hand. Because time spent thinking about a call counts towards a player's thinking time, and because thinking time is public on BGA, it is necessary to show, when a call is being offered, which player it is being offered to.
- It is possible to change your calling preferences during a game; however, due to technical limitations, the setting only updates the next time you "take a game action" (either discarding a tile, or making, or passing on a call). Remember this if you want to turn on/off chii/pon mid-hand.
- Also be aware that your 'preference' for automated passing affects ALL games you are in; unfortunately the preference cannot be configured differently for different games.
Even with those caveats, my friends and I have found that turn-based riichi on BGA, with automated passing enabled, is a real game-changer and an excellent option that fits with our lives extremely well.
For your scenario, since you are presumably playing with strangers, unfortunately all you can do is politely request that they enable automated passing (feel free to direct them to this post).
Automated passing was implemented specifically for turn-based games and I would never want to play a turn-based game in which players were not using automated passing, however, it is a choice that each player needs to make (particularly with the hand-revealing problem in mind).
In terms of leaving the game, once you join a game on BGA, that is meant to be a commitment to see the game through to its conclusion. I believe this is displayed to you in a prompt before you join the table, along with the expected game length. I believe expected game lengths of riichi can go into multiple months depending on the turn timers.
If you quit, your reputation will be severely impacted and your turns will be taken by a draw-and-discard bot, affecting the game for the other three players. If at all possible, you should see the game through.