I'd consider returning that iPhone and ordering one with more internal storage, as you've already bottomed out your usage, and that's not going to improve over time. Apple allows 14 days to obtain a full refund.
Other is not something there's much control over, and—on macOS—Apple indicates it is what it is: "Other: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files and other runtime system resources. Also included are temporary files, fonts, app support files and plug-ins. You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac."
On iPad and iPhone, here are the contents: Other: Non-removable mobile assets, like Siri voices, fonts, dictionaries, non-removable logs and caches, Spotlight index, and system data, such as Keychain and CloudKit Database. Cached files can't be deleted by the system.
On iPhone and iPad, here are some suggestions for reducing it: https://ioshacker.com/how-to/free-other-iphone-storage
But for many of us 64 GB is going to be tight, regardless.