Did this happen immediately after you set up your Premiere, or was it fine for a bit, and then happened? Does the video play fine in a selected app?
From what I have gathered so far, a few people with the Sony Bravia had some static and other display issues when they used Auto-detect during the setup (with different streaming devices). They solved it by doing a factory reset and not doing the auto-detect but manually assign the display. Some chose the 720, some chose the 1080. (I would choose 720 for initial setup when prompted)
Before doing the factory reset, try unplugging the HDMI at both TV and the device and plugging either back in or at another HDMI port. (assuming you are using the new HDMI hat came with your unit). If not already, power your Premiere from the wall, not the TV (the power supply boards on these TVs can be finicky enough to cause interference.) You may have just had a corrupted setup.
If you end up having to do factory reset, try the manual 720 first, then redo at manual 1080 if unsuccessful. Settings...System..Advanced System Settings...Factory Reset
Before doing factory reset check the simple things (the hdmi cable setup and power supply of Premiere). Another thing of note is that the Bravia's reset timeout is 10min to drain residual charge (Unplug your TV for at least 10 min.) Sometimes, it really is the simple things to try first.
Problem began immediately or close to it. I did use autodetect so that may have been when it began. I was not really paying attention to the display quality during initial reset. The video plays fine. No problems there. I will try the rest of the suggestions.
If you have do not have another tv to test the Premiere on, I think you have exhausted what can be done on the Premiere itself. (It still could be the Premiere unit itself, but without testing it on another TV, no real way of ruling it out.)
Now you are left with seeing if there are any settings within the TV itself that can be contributing. It would likely be under the Video or HDMI options under your TV Menu settings. There may be a Resolution or Display Setting mismatch. There is also a manual Factory Reset option depending on model.
If you can provide the actual model number of your TV, would be able to look into it a little bit further. The standard troubleshooting for Bravia did not show the actual pixelation you are experiencing so it did not show a standard solution step. Here is kind of where you try to plug in a DVD player, or a laptop via HDMI cable or change the HDMI cable itself to see if you are getting similar results to the Roku.
For some of the Bravias, there is a custom mode and standard mode. Standard is usually fine, but in custom you can turn off a lot of advanced settings, eliminate noise, enable HDR.
Kind of down to determine if the Premiere or the TV itself is the problem. Process of elimination through different tests. Other option is to pick up another Premiere at Walmart or Best Buy and just plug it in. If same results, then you now know it is TV related.
Take a look at this link (not model specific) but does a general walkthough of using Bravia with attached devices and the seeting you may have to change. The link is actually page13, so read through his article and see if any of this is helpful. Note the settings you may have to make at each HDMI connection to make a device function. https://www.tomsguide.com/us/sony-tv-settings-guide,review-5605-13.html
Tried alternate Roku Premier on the original tv. Worked perfectly. Tried original Roku Premier on alternate tv (Samsung). Had the same pixilation problems as first reported. I am thinking the Roku Premier player is defective. It was purchased very recently from Roku. How do I proceed?