How to enable TalkBack through ADB in Android P?

I've got the Oneplus 6 with unofficial mod (OmniRom Treskmod) installed on it. The issue is that the mod probably uses its own setup programme, and the accessibility gesture is partially broken. Holding two fingers in the middle of the screen starts the accessibility mode, however, it enables only some particular sounds such as those heard when locking the screen, but TalkBack doesn't start speaking then. In earlier versions of Android there was a possibility to enable TalkBack through [tag:adb] by editing Settings.db but I guess something has been changed since then and the method is useless now. Do any of you knows the way of enabling speech through adb in the latest Android version (Pie)? What I want to achieve is to have it talking right after reboot. Of course, I know I could ask sighted person but I'd like to know if there's any solution to do it on my own. I faced similar issue with Lineage as well.