I can confirm that the trainer 0.11c does in fact work for The Forest version 0.12, but complications arose before I could get it to work,
1. my copy that was in the Steam Forest folder had vanished, I located the .rar file and attempted to replace the file within back into my forest folder, this would not work,
2. I checked the Avast antivirus exclusions and found it missing, I added it once again, and it still refused.
3. I deactivated Avast and re-downloaded the trainer, placed the trainer in the Steam/The Forest folder and placed a short cut on my desktop, I entered the game and activated the trainer with F1 seconds later I heard a ding sound, then activated F2 F3 F4 and F5 I did not plant a blueprint and used one resource as this never worked for me, after activating each one and heard the words cheat activated I placed a blueprint of the full cabin, approached it and it built immediately, then I added large effigies and all went well, then I alt/tabbed to desktop to see the trainer, and noticed that F1 was not showing activated, all the others where in red and ticks in the boxes, but not F1, so for some reason Avast will not allow the trainer, as soon as I reactivated the Avast antivirus my trainer vanished from the Steam/The Forest folder it was in, and the folder was no longer mentioned in the exclusions, so figure that one out, but the trainer worked, that's what I am saying, a little workaround and off you go, I am not saying that doing it as I did will get it working for everyone, but it works for me as I am sure it will work for others...Good Luck