Or instead of installing some other app you know nothing about, you can just download the google map area for Offline Use, for where you are going prior to needing it (or turning off your cell data), as an example, I just downloaded the map for Rome, then I can turn off cellular/WiFi and still use your phone for navigating that area when there, That can be anywhere in the world, you don't need to be there yet (although I am not sure the Chinese/North Korea allow that, but probably everywhere else allows it)
I often do that from home prior to going to somewhere I am not sure how the signal will be, or if I want to reduce the cellular data usage while somewhere I might have to pay extra for it, like when I head to Europe next spring.
Years ago, prior to getting Starlink early last year, we drove our Motorhome down the Cassiar Highway (2019}from the Yukon toward Prince George BC, 500 miles of no cell signal (was the exact same on the 2023 trip) I downloaded that whole area while in Alaska with service and the navigation worked perfectly. Fast forward to the 2023 trip down the same road, we had Starlink In-motion Dishy mounted on the roof that gave me phone and data the whole trip which was amazing to say the least! But I still downloaded maps for the whole area just in case Starlink didn't work up there, it was an unknown to me at the time.
Below is the HowTo..
To download a map of somewhere from an iPhone open google maps, click on your icon (top right) about 1/2 way down the list that comes up, click on Offline Maps, click on Select your own map, mine always defaults to where I am, so I scroll around to find the area I need. (often I zoom Out first to make it quicker to get to the area) Then you can zoom back in once there (pinch your fingers together or out to change the size of the map you want to download) Once you are satisfied with the area you need. (there is a limit to the area, so you may need to download more than once) Click download map. It can take a bit and will continue in the background on WiFi, you can turn on downloads via Cell Data if you want to. Once its done, I often rename it so I know what it is and can delete it to free up space on the phone when its no longer needed. You go into offline maps again to remove them when you don't need that place anymore. You can also update it just prior to going there if you downloaded it long before traveling.
-Bill