[Xperia Z3 Compact Android Development] okij:
Installation instructions

Hi [MENTION=8665569]gutingi[/MENTION] and welcome on XDA. :)

Since noone answered you yet, I digged in the threads and posts that are useful for installing TWRP and rooting on Z3c with locked bootloader, TA backup, bootloader unlocking, installing TWRP on device with unlocked bootloader, etc. and would recommend you the following procedure:

Installing Sony's ADB drivers won't hurt, but it might not be necessary if you already have some ADB drivers on your PC from flashing your Samsung tablet.

Since you are already on the latest .291 firmware, follow [MENTION=4688377]russel5[/MENTION]'s guide Recovery & Root for MM .575 & .291 LB to install TWRP and root your Z3c.

Backup your TA partition according to [MENTION=5293862]Depressed T.Bear[/MENTION]'s post found here.

From your post, I get that you didn't use your Z3c yet, so you don't have personal apps and data on it. Otherwise, you should now make a full TWRP backup, as well as a backup of all apps and system settings via TitaniumBackup.

Unlock your bootloader according to Sony's instructions found here. You can use Flashtool to do the actual unlocking, but also for this you need the code that you get from Sony.

Flash [MENTION=4675360]tomascus[/MENTION] TWRP twrp_z3c_2017-04-26.img from this post to the FOTAKernel partition. I recommend you to use this TWRP version (3.1.0-0 to be exact), since I didn't have any error 7 problems with it. You can also find some slightly newer versions (3.1.1-0, maybe 3.1.2-0), but I would stick to 3.1.0-0 because it works fine.

Reboot the device and press Volume-down when the notification LED turns pink to enter TWRP.

Do a full wipe (Dalvik / ART Cache, System, Cache, Data, Internal Storage)

Flash the ROM (CARBON-CR-5.1-MOO-RELEASE-z3c-20171018-0207.zip)

Flash the latest Gapps 7.1 (Open GApps is a good choice. I personally prefer the Aroma version to install Google Dialer etc. right away. The Nano version should be fine as well, but if you should have mic issues during calls, please read my post here.)

Flash [MENTION=4275152]someone755[/MENTION]'s Kernel12 r_11.zip (If for some reason it doesn't work for you, e.g. you get a bootloop, you can push Power, Vol+ and Vol- buttons all at once for some seconds to power down the device, and then start from #7 again without installing Kernel12. The default Carbon kernel is working fine as well.)

Flash Magisk v14.0 if you want to root your device (you could also use SuperSU, but Magisk is much better IMHO and according to many other users)

Reboot and wait for the first boot to finish (you will see the animated Carbon logo for about 5-10 minutes), then you can set up your device.

Good luck and please leave some feedback if everything went well. :)

I wrote these instructions to my best knowledge. However, it's been a while since I did those steps myself and I cannot guarantee that everything is working for you right out of the box. If you should experience some problems, please ask for help at the according threads first.

It's really difficult to hard-brick a Z3c. The only cases I read of were users who flashed a TA backup from another Z3c to the TA partition (so never do this!) and some devs testing out some weird stuff. If you follow the instructions, you should be safe and shouldn't be afraid to do these things. If for some reason you want to revert to stock ROM, you can use Sony's Emma tool and of course then you should restore the TA backup you took in step #3 (I personally didn't need this or try this yet, since I'm happy with CarbonROM).

Please leave some thanks at the dev threads that I linked you to, and if everything goes well, you could make some donations to the devs, they deserve it. :)

I will be on vacation for the next couple of days, so - even though I will follow this thread - I might not be able to help you if you get stuck. I hope that some of the other users will step into the breach then. You could also ask for some help at the LineageOS or Resurrection Remix ROM threads, since the steps for getting a custom ROM up and running are always the same and they have some helpful guys over there too.