The patch should be that .zip file referenced when using the adb sideload command on your computer. The “Advanced > ADB Side load.” Is a command in your recovery (/e/ recovery or Team Win Recovery Project “TWRP”). Basically, you use the Linux terminal to send the zipfile to your phone ("side load"ing the zip file) after your phone has been set to accept the file while in recovery mode. From what I gather you are not looking at the right thread for a fresh e install on a S9 though. See below.
Edit: > HERE is a link for how to do all steps on a S9 specifically. Be sure the /e/ ROM you download is for Android Q/10 as it has to match the version of Android on your stock ROM (you mentioned your new phone is on Android 10/Q currently).
Edit: In the previous paragraph you will find the /e/ ROM for Android 10/Q listed as " * /e/OS build : dev" NOT “Stable” this is for phones currently running Android 8/“Oreo”
If I was in your shoes (I was not too long ago) I would take sometime to read through everything listed in my original link or buy direct from e. Good luck!
Have you removed all accounts, passwords, fingerprints, etc. from the stock ROM before moving forward with the e flash? If not, this can cause issues. I am not 100% sure on this specific “Error: 1” but think it could stem from not removing the said protections.
after >wipe >Format /Data, tip yes,
go back to the main menu, choose reboot to recovery
you can try >wipe >advanced wipe >select /preload, swipe to confirm.
and retry to apply the patch,
in the offficial documentation it is not clear ( why this /boot patch ? only for the s9 ! when apply it ? )
it could be unusefull now, it could be for oreo-stock-firmware ? or for TWRP 3.3.x-x ? or for TWRP 3.4.x-x ?