I'm not sure what I'm legally allowed to share while under an agreement with TAKUMI JAPAN 株式会社.
Additionally I am not responsible for ANYTHING you choose to do with your device.

If you choose to modify your device, you risk permanent damage, and most likely void your warranty.

Working USB Debugging through ADB is in fact possible, under specific conditions.

There is some limitation placed on the USB debugging authorization prompt on some firmwares.

this limitation is present on the prepaid version's (KAZ-F019) software version F019_R031 but is not present on the postpaid unit (KAZ-F119) version F119_R024.

It is possible to flash a prepaid KAZ-F019 to a postpaid KAZ-F119 if you can locate the firmware package

this can be done using either the Qualcomm Flash Image Loader (QFIL) or through Verizon Software Upgrade Assistant and a bit of quick thinking during the download phase right before the device is "repaired".

I can not guarantee that everything will work as expected after flashing your eTalk as the postpaid variant.
They dont seem to have any meaningful differences between the two save for software version but you can never be too cautious.

If you do decide to go this route, backup your IMEI, because recovering it is a real pain.

My particular unit was purchased as "unlocked" and still detects my SIM correctly but your mileage my vary.

Enabling Developer options and USB Debugging:

Authentication pop-up

Launch the Engineering Mode app by inputting the dialer code: *#*#825864#*#*
Click on Developer Options, and toggle the category to make changes.
Scroll down to USB Debugging and toggle it.
If you have and ADB server running you should see your computers RSA fingerprint. You can select "Always allow..." and click OK.

You now have working ADB access and can install any supported application.

Note on application support:

Apps4Flip launcher

The eTalk seems to share common DNA with the LG Classic Flip so anything that runs on it should run on the eTalk as well.

if you choose to install the Apps4Flip launcher choose the one for "LG Classic Flip"

There is no restriction on the application's namespace or signature and I was able to load a wide variety of apps, though I was limited by the devices general hardware.

The accessibility enabler app xxdeafgirl shared works like a charm, as does list launcher.

Misc findings:

QDLoader 9008 Mode - Hold Volume Up while plugging it into your PC.
EDL Deep Flashing Cables work too.
Recovery - Volume Up while booting (not much to see here)
Fastboot - Volume Down while booting (or here for that matter)

Treble Compatible
Still working on getting a custom recovery working (hopeful), or unlocking the bootloader (less hopeful) but once we do, it should be possible to completely replace the version of Android with a custom one. Maybe even KaiOS...

FM Radio
I believe the FM Radio to be enabled across all eTalk models, we just need an app to utilize it.

Factory Test Utility
There is another factory test utility, this one baked into the boot image itself.
It's accessible by holding both volume buttons while turning the device on.

Nothing particularly interesting here. You might not even be able to reboot out of it.
2/10 would not recommend

Wrap up:

Hope you found this helpful or at least interesting. Let me know if any other mysteries pop up.

Cheers,
Dan