I'll help you figure this out. The in-app camera in Lightroom Android takes the default resolution of your mobile's camera into account when you take images.
Are you shooting from the front camera or the rear camera? What device & Android are you working with?
In the in-app camera, try changing the file format between JPEG & DNG from the top & compare the results. Images taken from the front camera in JPEG will likely be 1080 X 1920.
Features like having Lens controls in the Lightroom in-app camera are open for feedback & upvotes here: https://community.adobe.com/t5/lightroom-ecosystem-cloud-based-ideas/p-ability-to-select-lens-on-lightroom-camera-app/idi-p/12778619
Let me know if this clarifies this for you. Thanks!
Sameer K