I found the "Official" thread at avsforum.com for your model. One guy had the same issue two full years ago (August 2017) but no one responded to his issue. He said he was bringing it back to Best Buy to swap it out. Link: USB Power Issue
Here's a thought - Even though you're seeing that message, there's a chance that USB, itself, might still work. What about manually downloading the latest Roku update for the TV and put it on a USB stick and forcing it to "upgrade" (actually copying the same version over itself)? Maybe something in the Roku update got hosed while installing, resulting in this message, so if it allows you to essentially refresh itself, try copying the Roku update to USB and install it.
Here's the download page: (You have to use the model number Roku has for your TV in the "About" section - specifically "The Roku Model Number can be found on the Settings > System > About screen on the Roku TV. It’s four numbers and a letter." It looks like it should be 7103X
as the model number. Roku Download Page
This page will walk you through the steps after choosing TCL as the make and 7103X as the model.
Here's the TCL how-to about manual firmware/software upgrades. It does say on this page that you might get an error if it's the most current version of software already installed, but give it a try. How To Update Software On TCL Roku