I was in the same boat. Don't quit right away...suck it up for a couple of years.....switch firms/ practice area if you have to so that it gets a bit more bearable. If you find T1 too toxic, get into a good T2 after 1-2 years in T1 and getting good in your practice area. During 0-3 years keep aggressively thinking of an exit strategy from law firms....anything that appeals to you and makes sense in the long term. Not necessarily in-house...not necessarily even law...can be anything where you make enough money to suit your lifestyle and circumstances and can be at peace with yourself and do something you enjoy long term. Think hard about what you really want to do and how it can be feasible. Think in terms of overall sustainability....not just immediate/ short term relief from your current job. Once you've really sorted out your exit plans, quit the law firm industry. Spending a couple of years as an associate at a tough law firm builds some transferable skills which can be applied in other jobs and industries where most people really lack these skills. So, learn what you can while you are in a toxic law firm job, because even lessons learnt from such places can prove to be very useful in life later on.

This very feeling is when you should know it's time to quit - " I’m burning out, don’t see the point. My health is suffering and I’m so anxious all the time. Every outlook mail fucks with me, every teams notif makes me want to run." Try to find other firms with better seniors who won't make you feel this way. I've been in both situation, it's not the work but it's surely the people you work with. And if not firms, then definitely in-house but run asap. You will feel a lot better mentally and physically, trust me.