Thanks for reaching out. We are here to help.
Could you please confirm the version of Lightroom & the operating system you are working on? Are you using Lightroom Classic, Adobe Lightroom Desktop, or Adobe Lightroom mobile (iOS/Android)? Are you shooting RAW images from a camera or using an Adobe Lightroom camera on your phone?
If the exported image is converted as JPEG, it is expected as JPEG will be suitable for sharing and circulating as an output, while RAW images are not universally compatible.
To learn more about this, check the below-mentioned articles:
Adobe Lightroom Mobile (Android): https://helpx.adobe.com/lightroom-cc/using/save-share-export-mobile-android.html
Adobe Lightroom Mobile (iOS):https://helpx.adobe.com/lightroom-cc/using/save-share-export-mobile-ios.html
We hope this helps,