I am a bit surprised at some of the comments here. I'll start by saying that I only have one side of the story so it is possible that the way you suggested those changes is the problem and not the changes themselves.

But, having been in a somewhat similar situation, I can tell you that some companies and teams are just dysfunctional and "cliquey". It has nothing to do with anything rational or logical or something you did or didn't do, it's just broken beyond repair. My guess would also be that they have had a number of people come and go probably due to the same reasons.

That manager also sounds like they shouldn't be managing at all. Besides that silly metric(did they also specify how many lines of code they want per day? ridiculous), it would've been more useful if they explain why your changes were turned down at least. There might be a good reason that you're not aware of. A sane manager would choose to guide you to make sure your valuable contributions benefit the business and align with any strategy as opposed to talking to you like a child and going "do it because I said so". Your teammates may have been having a bad week or feel threatened but I blame your manager. They should know better.

I recommend you plan your exit as nothing good will come out of you staying.