When I was testing the upgrade of the s9 from /e/ Oreo to /e/Q I did the following
- Downloaded the Stock 10 ROM from sammobile for india …country where I live
- Downloaded the ODIN ver 3.14
- Removed all pins and locks set up on the phone
- On a windows PC installed stock 10 first
- Checked the phone was working on 10
- Installed TWRP
- Installed a patch we have linked here by sideloading as described here
- Sideloaded the /e/OS Q build
Had done this a couple of months back to test a few different options and hope I remember the steps correctly
I have asked a team member to update the s9 / s9+Upgrade page as it is created using a template and is incorrect. …mentions Fastboot which does not work on Samsung devices.
If you check the LineageOS wiki they sideload the upgrade OS for all devices
We are working on getting a OTA OS Upgrade working for the s9 / s9+ . This development is still in progress.