My worldwide vegan experiences are kinda limited. I was only vegetarian in China, so I can't speak to the vegan experiences there. Pure Lotus in Beijing was probably the best vegetarian place in the world that I've been, though. I expect they have a lot of vegan options, but I really don't know.
In the Western hemisphere, I've heard REALLY great things (and seen really great videos) from the Maravilla guesthouse in Puerto Rico. It's a tiny little husband/wife operation (ex-husband and ex-wife, I guess, now?) in PR.
The people that I know who went were greeted with amazing staff who are now lifelong friends with them, amazing food, awesome views, etc. They went for a honeymoon. I'm probably just going to drag my girlfriend there for valentine's day because I'm dying to go visit for myself.
Try "HappyCow" app. It's great for finding vegan places or places with vegan options.
If you have an Android phone, you can get it at https://play.google.com/store/apps/details?id=com.hcceg.veg.compassionfree
I already have paid for and use Happycow. I have an Iphone, but I am wary to install yet another app just for vegan food in NYC when everything is likely already listed on Happycow already and probably more up to date there.
>then marking the ones that interest me on Google Maps.
That seems laborious. NYC has so many vegan spots and spots with vegan options, that I can't see myself doing that.
You can try Komoot for free but if you want to use it long term, you need to pay for some kind of map pack:
https://www.komoot.com/product
I just paid $30 to unlock the whole world back in 2018, but I think it was worth it. I find it is easier and more accurate than either Google Maps or Apple Maps, You can download maps locally to your phone, but to actually plan and create a route you need to be online.
I haven't been but the book Japan: A Travel Guide for Vegans by Jesse Duffield would be super helpful! I haven't read the Japan book but I read the author's other book on Taiwan and it was insanely thorough, with recommended itineraries and vegan places to eat nearby, history (including of veganism in the country) and of course tons of restaurant recommendations. So I imagine the Japan book would be the same!