I always used "adb install" to install programs on my phone from my PC. I never heard of the "adb sideload" command, but my search results [1][2] indicate that the second command is for installing things from the recovery mode, when you don't have the full Android system running. So "install" is the command for installing programs under normal circumstances using the Android installer.

[1] https://android.stackexchange.com/a/84248

[2] https://www.androidauthority.com/how-to-use-adb-android-3260...