Manual flashing

Sometimes you just need to flash ready system image externally. Export the images that pmbootstrap generated with  and read on, how to call the flashing application from your host OS.

Fastboot
See, and expand this section if you find out something that would have helped you.

LineageOS Recovery can be flashed with Odin. From LOS Recovery you can enter userspace fastbootd to flash .img files via fastboot. This was implemented in Android 10, provided the recovery supports entering into fastbootd. Yes, fastboot on a Samsung device. Tested and working on Tab S5e, but should work on all Samsung from A10 + with supporting recovery.

Odin
Odin is an official flasher for many Samsung devices, runs only on Windows. Make sure you have the latest Samsung USB drivers installed before plugging in the smartphone in Odin mode.

To flash your phone with it you will need .pit file containing information about all partitions, you can find one online or download it from the device e.g using Heimdall.

Heimdall
Heimdall is an opensource alternative to Odin that runs on Windows, Mac and Linux and can flash many Samsung phones. Be aware that Heimdall doesn't support some Samsung phones (usually that uses different file than .pit).

The user grimler maintains a Heimdall fork here with some additional patches, since the development at the official repository has stalled.

Easy way
Use heimdall-frontend

On tab Utilities you can obtain .pit file from the device by choosing save location and clicking download

When you have .pit file and required img files you can go to Flash tab, select your .pit file, add new partition, configure it (name and flashed file), optionally add more partitions and click Start to flash everything to the device.

Hard way
First, turn on your phone in download mode (You can use to see if Heimdall detects it.)

To download .pit from the device:

When you have .pit file and required img files you can flash your device with:

You should be able to flash several partitions at once

Flashing TWRP can be done in the following way (change filepath to the location of your twrp):

heimdall flash --RECOVERY ~/twrp.img --no-reboot