plagiarism - Professor does not care about cheating, what should TA do?

I am a PhD student, working as a Homework marking TA in a school where cheating is extremely blatant. The university has an extremely strict policy against cheating. Hundreds of students in math courses alone are reported each year, and suspensions are given to severe/repeat offenders. I have personally reported cheating many times.

Based on this environment, most courses have shifted away from Homework grades, and more toward Quiz/Test grades.

My course is a low-bar mid-level math course, very likely to be the last math course ever taken by the students who enrolled in the course.

The marking distribution of my course is done in a way where the homework mark weight is so absurdly high that cheating on homework would almost guarantee a pass.

I had realized this at the beginning of September, and discussed with (confronted) the instructor. The short summary of the response is that the instructor doesn't care about cheating.

The professor doesn't want to put in the effort to deal with cheaters. The professor thinks the students cheating would not be overly unfair to other students who don't cheat. The professor also does not want me to try to catch cheaters.

I have made clear that cheating on homework almost guarantees a pass, and he/she agrees, and is ok with this.

The homework are all questions from the textbook, and a solution manual is readily available on google.

In this week's homework, I have found more than 100 students who have copied from the solution manual, where at least 50 students copied word for word (if reported, the cheating done can be easily proved by the school.)

I suspect I only caught a portion of all cheaters, as buying solutions at this university is too blatant.

I would like to ask the community of my next steps.

If I were to report the cheating to him/her: Would I anger the professor, since this is against his/her wishes? Would I build a tense relationship with him following this? (There is still a whole semester ahead, and possibly years in the same university.) What would be done in the end? What if he ignores the report, what should my next steps be?

If I were to report to the undergrad chair: Would it be inappropriate to skip reporting to instructor first? Would I also build a tense relationship with the instructor by this move? I am almost positive that there would be action by the undergrad chair on the cheating behavior.

I could also report to both simultaneously. I could also do nothing at all, in which case the cheating would without a doubt continue for the whole term, with the vast majority of students taking part.

I personally disagree with the professor, as I believe that it is unfair for the minority of students who don't cheat. Due to the high homework marks, a mark curve is highly unlikely, so the students who don't cheat are truly getting lower marks because of the cheaters.

The instructor is in the beginning of his/her career, and not retiring. The university is in North America, very large (more than 50,000 undergrad)

Edit3: As I continue to grade, I have found more and more cheaters, in the hundreds, approaching 50% of the class.

Thanks for all the suggestions asking me to "let it go". After much consideration, I can not take such advice.

Thanks for all the suggestions of asking me to "not skip the chain of command". I have since realized this may have severe consequences, and have decided against it.

I have contacted only the instructor with minimal details of the situation. Thanks for all the support and best wishes from the community, I sincerely appreciate it.