OK … a couple of things …
10.x.x.x is probably the address the modem sees because you are behind CGNAT – carrier grade network address translation. Carriers typically employ this strategy unless you have (and paid for) a static IP address. Rationale (over-simplified): “security” and because there are a limited supply of IPv4 addresses. (Search on this forum and the internet for this acronym – it’s been widely discussed.) So, in this case the “ten dot” address was likely assigned by your carrier and it’s “OK.” However, as you have observed, it’s not route-able – except to your ISP. Once your packets arrive at the ISP they’ll be magically “turned into” route-able packets sent to the internet.
Now … to your original question … I’d invite comments from others as none of our SOHO customers are using a USB modem with that product so far as I know. However, I can tell you Peplink has been responsive to requests to provide this information to users of other routers. Here’s the screen from a Balance 305 which shows the metrics from the attached USB modem, for example:
If you don’t see a similar panel on your SOHO you may wish to submit a request in the appropriate section here on the Forum. (Remember, the SOHO can only use one WAN at once so ensure the WAN with the modem attached is active.)