This is exactly what I did for a Galaxy Tab S6 Lite, as detailed at this post. It has worked, and it’s chugging along with /e/, now matching my phone, allowing me to finally leave the Apple ecosystem. 
The trick was to forget about the OEM Unlock option in Developer options, since this was not reliable – sometimes it was there, sometimes not. Instead, I booted into Download mode and selected Unlock mode to unlock the bootloader. It did its warnings, but unlock went off easily.