I'm a new PLO player trying to build a bankroll online. I found a soft game at IDN site and set up a 30-buy-in grinding project.
(there are a ton of players spewing chips like monkeys, that's why I think the game is soft.)

After 7k hands, I found that I have a problem with an AAxx hand all in pre-flop and a silly draw like

I have AhAd6s5h IP on the turn villain has QcJh4c2c, I bet pot, he called on the board 7d9cQhKh trying to draw the T.

or something like

I have AcAs9h7h OP bet pot pre-flop get raise to all in pre-flop by Kh9s8d4d and the board open Ks6hQd2h9c, he got two pairs.

Another case would be I missed the 13 or 16 cards straight draw on 1/3 pot odd. (no flush redraw go with 13/16 straight draw)

Assuming that the RNG of IDN site is ok, after playing for 7k hands, I face a downswing in the picture. (20k chips for 1 buy-in, then)
My win rate now is -20 BB/100(very bad, I knew) and the win rate for all sessions is 0.64.

Any advice, please? Is there a gap to improve or my bankroll is not adequate for the game?

I'd quit the site before you lose it all, not looking good for you. Find a better game.

This site has tools to look at win rates and variance: https://www.primedope.com/poker-variance-calculator/

7k hands is not that many. You might find there is a decent chance that you could be a winning player on a downturn. Or, you may need to improve your game. Also consider how the rake structure might be affecting your win rate.

If getting re-raised all-in preflop by Villain with K984ss is typical for this site, then its hard to imagine a softer site.

In your other hand, 79QK is a terrible run out for aces because Villain's range is supposed to contain many Q and K. You should not have been aggressively betting this board.

Please tell me why I should quit. I thought the game here has full of money monkeys.

Seems I can improve an aces one-suited play on the gut shot drawing board, today I also found players that always draw just a gut shot all the session.

Slowing down the play help to protect lose from the suck out.

Could be cheating…always a possibility.

Found some thread about RNG of this site as you said. However, I can afford to lose this bankroll.

I just want to say do not underestimate how important it is that all 4 of your cards work together. You absolutely must be making combo draws and not 'mutli-draws'. A multi-draw is a hand like AA56, which is basically just 2 different hands entirely. You dont want to be hoping to hit a set or some kind of straight draw, because thats all you will ever improve to when you connect. You want to hit a straight draw that can improve to an even better straight draw with a backdoor flushdraw to go with it. A hand like AAJT is much better since now at least the AJ/AT work together. PLO requires as much patience as NLHE imo to get these kind of hands, despite how bad you see your opponents getting paid off with naked KK.

I just passed the 10k hands and add chips to 50 buy-ins for handling the downswing.

The Win rate is still negative and the graph is flat, still trying to beat this soft game.

I dont know man, what do you want?
Impossible to tell how you play, but you only post some examples of bad beats. Of course, the variance is high in PLO, could be that you are a winning player just on a downswing, but also likely that you have several leaks to fix in your game overall.
I can tell you, getting it in with AA against K984 pre is not a leak, so why post it?

whats the x axis in your graph? if its sessions played, you would have played 300 sessions to reach 7k hands in your first graph.

Well there's only a couple conclusions

1.You are not as good as you think
2.You've hit insanely bad variance
3.The players are very good


Figure out #1 first as for most this is the problem.

I know the hand I post is a bad beat, I just want to know how to improve from what I observed other bad beats losing hands be like...

Flopped top set with bare set on board Ah4dTs and multi-way pot.

I had AsAd5d5h I bet pot on SB and BB raise pot with KdJc6s4h

UTG called with Kc8d7d6c

Button called with KhJsJh7s

I raised all in with the chip left and got a call from all of them.

turn 8h and river Qc made KdJc6s4h KhJsJh7s completely straight.

Yes, sometimes bad beats not happen and I hit the good draw like...

Board 4sKhTc6s on the turn

I bet pot with AsKcQcJs on SB

BB called with 9h9c7s4c

UTG called with Ts8s7d3h

CO called with AhQdTh4d

river 5s I bet pot again, BB fold, UTG calls, CO folds

The game is soft like that...

or another hand, this maybe my overplay...

I held AsTc5s3h on Button multi-way with

UTG AdTh8h4d

MP Qh9s8s5h

CO AcJcJh6h

everybody checked to me I bet all in and everybody called...

turn 8c

river Kd

UTG won...

In the first graph, it seems these happen along the way (10 buy-ins), I want to know that should I manage more buy-ins for these (that I add more as mentioned) or just improve my play.

I change the x-axis to hands played as below.

pretty easy to run bad over 10,000 hands. and yes -15 buyin downswings can happen in plo even to players with a high winrate. but you do probably have a lot of technical work you need to do on your game.

First of all IDN is one of the shadiest sites there is. I think people got superused there in the past on higher stakes. On the other hand loose spewy family pot games create massive variance so it is hard to tell is it the site or just bad run.

From Google: ouch!

Almost no PLO game is beatable at that structure. That's why there are so many fish compared to regs. But the only winner is the rake in the long run. find a new site.

Thanks for this info, could you please tell me why this rake structure is not beatable?