Re: Modern army meets fantasy

#10
This one is exactly like what you are looking for. Less of a focus on a single character, the main character in the story could be considered to be America instead of individual person.

https://www.royalroad.com/fiction/28654/america-in-another-world

Translated stories, which I know exist and have read some, but eventually dropped:

A dungeon core type story where dungeon makes technology like guns in a fantasy theme world
https://www.novelupdates.com/series/maou-sama-no-machizukuri-saikyou-no-danjon-wa-kindai-toshi/

You may or may not like this, it has the whole developed tech goes to undeveloped tech world theme, but for cultivation world type technology
https://www.novelupdates.com/series/miracle-throne/

I read a few chapters of this and didn't like it, but it fits your criteria, so maybe give it a try
https://www.novelupdates.com/series/modern-weapons-cheat-in-another-world/