The Samsung Galaxy S9+ (star2lte) and S9 (starlte) are upgraded from e-0.13-o-202012xx (Android 8) to e-0.14-q-202101xx (Android 10).
In itself, manually updating the OS with the TWRP Recovery already installed on the device is manageable by any normal user. It requires neither a host machine nor a /e/asy installer, but only the Samsung Galaxy.
The new /e/ OS ‘Q’ is downloaded as a *.ZIP file from the website, saved on the internal storage of the device or on a microSD card and installed from there using the TWRP function “Install”. After successful installation, a > Wipe >> cache/dalvik follows - and that should be it.
However, it is quite possible that the device starts in a bootloop after this update method. In this case, additional partitions must be deleted before flashing again, which involves a total loss of data.
If the LineageOS Wiki is to be believed, it is a basic requirement to also update the Android firmware before flashing the new OS - and this is a Samsung-Android-10-Firmware. This flashing process is no more difficult than the one mentioned before - but only for users who already know how to do it.
Before the installation process, regardless of the method, updating the TWRP recovery is also advisable. The new TWRP Release 3.5.0 has been available since the end of 2020.