The Chinese variants of Nokia phones, not only ship with a different and customizable build of Android but also they have their own apps instead of Google Apps. For instance, they have Nokia Gallery app instead of Google Photos.
Google has given up its services in China and as you probably know, all the phones in China do not have any Google Apps. This forced the Chinese OEMs to develop their own apps.
Nokia phones outside China ship with a pure form of Android without any bloatware and Google apps are the only thing added to the AOSP build. So, if you want a file manager app (of course, there is Files app inbuilt), you would have to download a third-party application. Why not try Nokia's own apps instead?
The following apps were extracted from the Chinese variant of Nokia phones:
- File Manager
I have shared these apks in the XDA forums. In case you don't like Google apps or if you don't want to use them, you can download these Nokia apps from the link below:
As you can see from the below screenshots, except the file manager all the other apps are pretty much similar to the Google apps which you already have. So you can download only the ones you want. The file manager has additional functionalities like displaying files in categories like Apk, favourites etc. And also shows the OTG storage if connected.