First things first, it's odd that a software lead is reporting to a project manager. Usually, a project manager works with the lead, but the lead actually reports to a development manager. Otherwise you end up in this sort of situation where your boss has a conflict of interest.
What to do?
First, hopefully you do actually have a line boss. Work with them to do their job. Engineering management primarily exists to protect their workers from this sort of abuse from project managers. If you don't have an engineering boss, then it falls to you. Ask to be included in scheduling meetings. Feign interest in the process, but once there - you need to fight for your group. If an estimate is unreasonable, say so.
If that fails, ask to meet with the project manager's boss. Explain the situation. Hopefully you have email evidence. Get other people this PM works with if necessary. Explain that this is leading to burnout amongst your team. Explain that it encourages cutting corners which will (has) harm(ed) quality. At first, frame it in business terms - the company could be doing a better job. Perhaps suggest working with another project manager if possible.
That though will likely fail. All the things you describe is in the PM's best interest. They look good to the boss, software meets their deadlines (so they must've been realistic), and all the side effects on you are immeasurable. And honesty, you're unlikely to get them fired since they're better politicians.
So send out your resume and be sure to warn HR during your exit interview.
