*UPDATE*
Burial's latest GCam_7.3_Burial_release_beta_10 also works with 4k video using telephoto with the renamed package from the info from KosBeg. I renamed it myself to something different from Wichaya's so Burial and Wichaya's can be installed at the same time. I have attached the renamed Burial to this post along with the XML for telephoto.
Thanks to KosBeg, we now know that these specific package names are whitelisted by Samsung to be able to use the telephoto camera:
com.sec.android.app.camera
com.sec.factory.camera
com.sec.android.app.camera.shootingmode.social
com.sec.factory.cameralyzer
com.samsung.android.bio.face.service
com.samsung.android.biometrics.service
com.samsung.android.server.iris
com.samsung.android.aremoji
com.samsung.android.ruler
com.samsung.android.scan3d
Confirmed all 3 rear cameras working with the S10/Note 10 series and S20/Note 20 series, front camera won't with OneUI 2.5+ unless you have S10 Lite or S20 FE.
Wichaya has also modified his GCAM for Samsung telephoto. Download the updated XML Wichaya file attached and the Samsung APK version from here
: https://www.celsoazevedo.com/files/android/google-camera/f/changelog1501/
Zoran's ZGCAM works best for Exynos phones. His latest will allow telephoto on Exynos Galaxy phones. Links to the latest gcam is here:
https://koopahtmaniac.com/getLatest.php . You can load the ZGCAM XML file I attached to use the 4x zoom.
Stock camera has improved greatly, but when it comes to zooming into the picture, stock cam's processing still does terribly with fine detail and edge smoothing. In my attached picture, the top is stock cam and bottom is gcam at 100% crop.
steps to apply XML to GCAM:
https://www.celsoazevedo.com/files/android/google-camera/f/settings09/