What’s the worst thing that could happen that would make you quit your job without having any other offers lined up?

[Long post warning]
I've 4YOE and I'm thinking of quitting my job due to various reasons, but I don't have any other offers in hand. I'm preparing well for the interviews, and have prepared DSA properly till now. But the system design bit is still pending, so I haven't applied anywhere yet. Due to work, I'm not able to focus on preparation and give time to it. I'm having just 3-4 hours of sleep on a daily basis as I'm literally grinding on the preparation side, but it requires more effort than this. My family has started worrying about my health and, after the EY incident, they are asking me to take my time and just go through the hassle of work, or quit my job if it's too much to handle.

I'm willing to quit my job right now, and I'm confident that I'll get an offer within 3 months, but I can't pull the plug on this, considering a hell lot of uncertainties in the market. I currently have enough savings to stay in Bangalore for at least 6-8 months. But still, taking this step seems pretty huge for me since it's my first job, and I've seen my parents'faces whenever I talk about quitting, it's not good.

Now coming to the reasons for quitting. I'm not sure where to start, and I'll not go into details. I just don't like to work here anymore. For the last 2 years, I've been working on shitty things which have stunted by growth professionally. The management is shit, and all they care about is deliverables and visibility. I've been a Java backend developer for the last 2.5 years, and before that I was a Data Engineer. I switched my team in the same company 2.5 years ago because I wanted to work on backend development and not on data pipelines. But for the majority of time I've only worked on data pipelines while being a Java developer. I've asked them a number of times in the last 2 years to put me where I have skills and interests, and every time all they do is make false promises of "good work" coming in the following quarter. I was willing to give my 200% into my work if I like it, but they just wanted me to work on whatever gets assigned to me and find my interests there itself. It's been going on like this for 2 years. Recently I had a connect with my manager, and he mentioned that the kind of work that I'm looking for won't be coming in this team, so either I should go to the other team (which is even worse in management), or I should just go. What's making me go mad is, it took them 2 fking years to tell me this? I got to know that they were not willing to let me go bcuz I was a good resource for them and, considering my experience with Data Engineering before, they were assigning me such tasks because I could finish those early without anyone's help. Other developers would have to learn about it first and then deliver. So, all this time it was actually possible for them to put me somewhere else, but they didn't. Now I've lost all my trust in this company, in my managers and the whole management. It's your job ffs to use me as a resource where I want to excel so that I stay highly motivated and productive. That'll benefit us both. But all they care about is how much I deliver and how much I make myself visible to the leadership for my promotion.

I've been depressed now, and don't have any will to go to the office and work there. I've stopped doing everything that a normal human being does to enjoy his day to day life, with a mindset that I'll do it later after I switch. I don't know what to do.