This. I recently hooked my steam deck up to a CRT (I’ve been playing a lot of games that were made for a 4:3 ratio). All it takes is an active adapter (in my case, active hdmi-to-vga) and setting the deck to output to a 4:3 aspect ratio.
That said, if that was a smart TV then OP would probably have a lot more issues. My parents have a (Samsung) smart TV and I’ve had nothing but headaches trying to get my deck to work with that, and they’re both modern devices. Some days it takes one try, some days it takes five tries, some days I just give up.