This month, I tried to upgrade my home theater setup with an LG C1 OLED television and an HDMI 2.1 receiver. Tried. In doing so, I discovered what a nightmare HDMI 2.1’s definition of “compatibility” is. When HDMI arrived on the scene almost 20 years ago, it seemed like a godsend: Instead of having to plug in five cables to get a 480p image with stereo audio, you could just plug in one cable. It was universal, had a directional configuration to make sure you couldn’t plug it in upside down, and it just worked. Two decades later, though, HDMI is alive and well but has somehow become needlessly confusing. Instead of a simple spec with complex cables, we’re now saddled with one simple cable and a truly baffling set of specs. Listen ye to my cautionary tale and beware the…