An important PSA regarding improving your accent in your non-native langauge:

This is not blatantly false—you can absolutely sound like a native if you put in the work. I've met countless L2 English speakers indistinguishable from natives, some are even close friends of mine.

While I know that people tend to be nice, I get asked if I’m Mexican ALL THE TIME without mentioning what sort of accent I’m going for. It’s definitely possible to change your accent, especially if you practice with people that are honest and point out what you’re doing wrong.

Not with that attitude lol. I mean, I'm a professor at a Japanese university, and we have a constant stream of nonnative speakers who easily pass for native speakers as far as superficial conversational skills go. Their writing tends to show some degree of non-nativeness, especially when they don't have time to edit their writing, like quick but semi-formal email. And they tend to have unexpected weak spots that betray them, like poor vocabulary in certain areas and limited knowledge of cultural references etc. But if you have a convincing accent, those minor errors and idiosyncrasies will be overlooked in everyday conversation, making you sound just like a native speaker. Probably, well-trained machine learning software can still pick up on a trace of their native phonologies. But, I'll be honest, as a native Japanese speaker, I only know that some of those near-native foreign students grew up in foreign countries because they told me so. If you're talking about near-native proficiency in all four major skills (i.e., speaking, listening, writing, and reading) at a very high professional level, it does seem to require exceptional talent and/or an extreme dedication. I only know one foreign-born person whose Japanese is, well, for a lack of better words, perfect in all accounts, from everyday informal registers to professional formal writing. She speaks not just standard Japanese but also the local dialect of the region she lives in with an authentic accent; no one even doubts she was born and raised there, although in reality she came to Japan when she was well into her adulthood. Anyway, if you only need to be good at accent, it's definitely possible for an adult leaner to achieve a level where they can fool unsuspecting native speakers in conversation. Whether it's worth it or not, I don't know. But I'm sure the "you should be proud of your accent" thing you talk about is pure nonsense for people whose accents are heavily stigmatized and discriminated against.

Maybe what you said is true, but it’s also a fact that people will judge your accent whether you like it or not. Some accents carry positive stereotypes, while others are tied to negative ones. It’s great that you’re working on perfecting your Japanese accent, and if you don’t look Japanese, people might even expect you to have one. In that case, having an accent isn’t necessarily a bad thing, which might be why you don’t see it as a big deal. But what if your accent were associated with unattractiveness or a lower social class? Would you still feel the same way? Not all accents are perceived equally, and that’s often why people go to the effort of faking an accent in the first place.

I agree it's unrealistic to sound 100% native if you are just starting to learn it once you are nearing adulthood. I've seen it time and time again. But there's also no need to sound native, it's good enough to just sound like you've been there a long time. You can usually just tell that someone is not American from non verbal cues as well, and no I'm not talking about the color of their skin.