I tried installing and configuring desktop environments for the PureOS, but it is obvious that there are compatibility issues, up to the point that a soft brick can occur when accessing the OS. I should have known of potential problems to arise for new builds. What was I thinking? I guess I got too hopeful.
At that moment, I had an OS boot installation fiasco. I even followed along the canon flashing solution(s), but apparently, serial, ethernet, workstation connection, and maybe a lack of detail is not enough to flash OS installation.
At the very least, my efforts to comb through the web paid off with success. If anyone ran/runs into the very same soft brick problem, I have found the working solution, at least for now.