non-EU Polish Blue Card guy - work remotely for German company?

This is the Germany forum.
But working in Poland (even remotely) is governed by Polish law and you need Polish permits/visa for it, not German ones.
So better post this on the Poland forum!

Your blue card would be tied to your work. If you have given up your job in Poland then you will no longer have a blue card. Is it somehow still valid for an additional 90 days after giving up the local job? I have no idea, maybe.  If you can still stay in Poland and work for a German company remotely, and for how long,  is a good question but needs to be asked of Polish officials, not on the German forum. But a blue card is not transferable. I doubt you could do this long term and keep the blue card. If you would move to Germany then you can apply and likely, but not guaranteed get a blue card here.

Have you completed two years in Poland on your first blue with your first employer?
If yes, it is highly possible.

if not, you will need to register for German residence to get the tax id activated. Then you can work for German firm. But, under this situation, I believe there is a altered law. you can check at https://www.auswaertiges-amt.de/