This HowTo is not suitable in all respects for upgrading from 8-Oreo to 10-Q on a Galaxy S9+ (hero2lte) and S9 (herolte).
The S9 / S9+ and stock Android 10 and therefore AOSP 10, on which /e/OS ‘Q’ is based, have limited comparability with lower Galaxy devices and OS versions.
In order not to lose TWRP Recovery, you should not install the recovery.img file - but I would not flash individual files, but use Heimdall to flash the four unzipped files AP_ BL_ CP_ CSC_ G965FXX*.tar.md5. In the process, TWRP is completely replaced by the stock Android recovery. But this is not a problem, because TWRP 3.5.0_9-0 can be very easily and cleanly reinstalled with Heimdall.