@audrew ADB is like a higher level of Fastboot. Basically ( please feel to correct me anyone) fastboot installs a boot image and a recovery image. The boot image allows UT to boot, but you usually have to manually boot to recovery. Once in recovery ADB is then working and the UT install will continue by pushing the UT files over it from the PC to the device.
A bad or incompatible USB cable will stop ADB from functioning so no UT install.
An encrypted data partition will stop an install and can be flagged as an ADB error, that is why you have to format the data partition to EXT4 and wipe it so it is decrypted.
If the partitions have been resized, usually by installing a non stock ROM such as Lineage OS, UT won't install and may give an ADB error.
A bad or USB 3 port may cause an ADB error.
A PC/laptop may cause an issue for various reasons, if UT won't install on Windows, try a Linux based machine or a MacOS based machine.
Try an older installer, the latest Ubports installer may be a bit buggy.
Also follow the installation instructions to the letter or the install usually fails. Try a different channel if the stable channel fails to install.