If you want to use an alternative launcher (user interface) on your LG smartphone, you not only have to install it but also set it as default.

Android 9 | LG UX 9.0
Step 1:  Open the  Settings
Step 2:  Tap on  General
Step 3:  Tap on  Apps & notifications
Step 4:  Tap on  Default apps
Step 5:  Tap on  Home app
Step 6:  Choose desired  Launcher
  1. Open the Settings
  2. Tap on General
  3. Tap on Apps & notifications
  4. Tap on Default apps
  5. Tap on Home app
  6. Choose desired Launcher

LG Instructions