I have this problem - I generally dislike fantasy worlds and science fiction set up in space or different planets. So I don't want to write about such things. I always loved more grounded stories about the real world. It doesn't matter if there is fantasy of science fiction elements in there, it is setting has to be close to reality as we know it, not the story itself. The common advice for writers in realistic setting is 'Write about what you know', but there is the problem. I really don't want to set the novel I write in my own country for several reasons. And I don't feel like I can realistically present a culture and everyday lives of people from other countries. I've done insane amounts of research over the course of my life, studying several foreign cultures. I can answer almost every question about several countries and their cultures. But that's just facts, you can't actually think like representative of another culture, you can't actually 'get it' if you never been there, in that environment. What should I do then? Try to invent a setting that looks like reality but isn't actually a real world? This approach seems cheap and even if it didn't, I'm not sure how to come up with something like that for it to not to cause repulsion.
"Write what you know" is a guideline, not a law, or every book would be an autobiography.
If you want to write about other countries, you say you've done a lot of research, which is a great start. That will keep you from making basic mistakes, like having your characters drive on the incorrect side of the road or dress inappropriately.
Beyond that, either visit the other country in question and get your own experiences, or find one or several natives of that country to act as your cultural nitpicker. Or both.
Unless you write to portrait life in a specific culture, fiction is mainly about people, and people are basically the same everywhere. Everyone wants physical safety, health, social connections, love, entertainment, and so on. People everywhere love their children, are jealous, strive for economic success, feel insecure or happy or sad. Since you are a human being and have spent your life with other human beings, you know how human beings work, and can write about what you know. Setting is just the background for the human drama, and as long as the setting is plausible to your readers (who do not live in the culture you write about) they won't care about the correct description of tax systems or public transportation as long as the descriptions of the people and their motivations and behavior are truthful.
Do not forget, that you do not have to include any details. Recently I saw quite below average thriller Donkey Punch which is being placed in Spain. But whole Spain serves just as background to the story and because it actually takes place on a yacht in the middle of sea, you could successfully move the story to Hawaii without any influence to the story itself.
I would recommend one better rule: Be creative. In one of my parody stories, I used Canton Tower as hideout of the bad guys. I do not know anything about China, or that tower in particular. I just liked the picture of it. And the setup of parody offered me possibility to use that.