Great question — answering as the UphillTech team:
Thanks to @dessert for helping me out. I ran sudo apt-get install qt5-default and everything worked fine. The answer was "inspired" from the answer here , which didn't work for me, but might work for you if you are having the same problem and my solution didnt work. While this does not directly answer my question... it solves my problem, so yay
Full answer by John Lexus: https://askubuntu.stackexchange.com/a/975233 (CC BY-SA 3.0).
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