Answer based on European standard where worker have some basic rights

• Not happy in the job : do the bare minimum while looking for something else guarantees that pay keeps coming, worst-case they fire-you giving you a severance pay (not necessarily big if you’re new in the company) and keeping your right to unemployment (which in general are lost when you quit).

• Toxic environment impacting mental health : Go to your doctor and take sick-leaves, and please do it before being in full burn out, then come back to previous point

• Very toxic environment, like harassment : Talk with a lawyer or an union representative you may have a case to sue the company, and even quit on the spot while keeping severance pay and unemployment rights, but you may-need a legal advise for it