Hello
I will try to share my experience on the install of /e/ Q on my Samsung Galaxy S9 (starlte - SM-G960FD)
Coming from Android 9 :
- Phone is a Galaxy S9 in Android 9 stock rom (for some strange reason, I was never able to upgrade in Android 10 via OTA), so I used it as with the security patches of 2019.
- I have some experience in using adb etc (as I used to install a Lineage on an old Moto E 2015 LTE), but i cannot be considered an expert.
- I decided to move the Galaxy S9 to /e/. (probably for the same reasons as you - more privacy - more battery)
On the road:
- I tryed to follow the install instructions on the site (which are not crystal clear as they mix O/Q version) and it was not successfull
- I used the Easy installer soft (0.12.3 beta) and it worked very well. The step by step is very well described. To my point of view, if you read the instructions carefully, you will succeed to install /e/ on a Galaxy S9.
- But I was a little bit desappointed to have installed an Oreo based version of /e/ (the stable version as per today - 11 june 2021-) . The /e/ Oreo works perfectly , but I wanted to install Q (still in dev) !!!
On the road again:
- I tried to install Q on top of Oreo (via the TWRP provided during the /e/ Oreo install ) but an error rised (saying that phone should be in 10 version to accept to flash /e/ Q) .
- I spent some time browsing and it seems that other people experienced the same (so its confirmed - not possible to install /e/ Q on top /e/ oreo via TWRP (at least today)
Back to Android
- I then decided to flash latest Android for my phone
- Get the latest ROM : use of Frija-v1.4.3 and download the 5GO of SM-G960F_2_20210511125707 (mine is XEF version for France)
- unzip the files (AP_G960FXXUFFUE1xxx.tar.md5, BL_G960FXXUFFUE1xxx.tar.md5, CP_G960FXXUFFUE1xxx.tar.md5, CSC_OMC_OXM_G960FXXUFFUE1xxx.tar.md5 and HOME_CSC_OMC_OXM_G960FXXUFFUE1xxx.tar.md5)
- Install the files with Odin3_v3.14.4 (for me AP, BL, CP, and CSC)
- boot to Android 10 : every thing went fine (just take care to finalize the process - download the latest files and patch via wifi, because in my case the OEM unlock only appeared then and was not available if installation was fully finished)
- go in development mode: OEM unlock, USB MTP file sharing, USB debug (you may have to plug - unplug the usb cable to auhorize communication and get the Accept USB message)
Install TWRP
- install TWRP with Odin : select the file (in the AP field) and start (twrp-3.5.2_9-0-starlte.img.tar downloaded from TWRP site)
- reboot in recovery mode (if you cannot boot in recovery then you will baev to do again the TWRP install process)
- if at any stage you reboot on system mode, the system will erase TWRP during its own boot. So take care to finalize the installation of /e/ without rebooting in system (staying in recovery mode)
Install /e/ Q from sideload: the easy 
part
- just follow the current manual
- tap
Wipe - now tap
Format Dataand yes - Return to the previous menu and tap
Advanced Wipe. - Select the
CacheandSystempartitions to be wiped and thenSwipe to Wipe - Sideload the /e/ .zip package.
- in the device in TWRP, select Advanced, ADB Sideload, then swipe to begin sideload.
-On the host machine, in the console , start the sideload of the package by typing “adb sideload filename.zip”
-Once installation has finished, return to the main menu, tap Reboot, and then System
The end!!
-Have a nice /e/ Q on your Galaxy S9 (or S9+)
Short summary of a successful installation of /e/ Q on Galaxy S9 (should be same for S9+)
- get the latest Android 10 installed
- via OTA
- via the Frija tool
Note : if currently on /e/ Oreo you will have to install Android 10 before !!
at least until /e/ and Easy installer allow the seamless migration from O to Q
- install Android 10 via Odin
- install TWRP via Odin
- Flash the /e/ Q rom
- Enjoy!!
Final impression
For the many that may be scared to do this somehow scary process, my personnel impression is that there is very little risk to break something.
Indeed the Galaxy S9 has a download mode that allow in any case to reinstall a stock rom on top of your work (during this test, i personnally reflash 10 times the android 10 stock version without issues before getting the final result : a Galaxy S9 with /e/ Q and TWRP )
An update of the doc may be necessary to make it clear that Android 10 is necessary to flash.
As the process with command line may seem difficult to some of us (it’s not), an updated version of Easy Installer is welcome.
Have a nice day
Regain your privacy! Adopt /e/ the unGoogled mobile OS and online services
and I had to install it manually from Odin and recovery.