• Yes that is a CRT
• HDMI to 3.5mm antenna is a non-existant connection and I will explain why and what you need to do.
• You will not like the look of any HDMI signal onto that tiny and cheap CRT (I own this TV and know)

Okay so any signal over HDMI is a digital signal, CRTs operate using only an analog signal (for the most part, there are some later digital sets). You would need to put your HDMI signal into a converter like this one. This transforms the signal into RCA/Composite. Then you take that signal and run it into one of these and then on the side that says To TV you put a coaxial cable from there to one of these. Then you take that and plug it into the 3.5mm antenna plug on the side of the TV.

https://www.amazon.com/CIMPLE-CO-Composite-Converter-Modulator/dp/B06XC9Y3VB

Appreciate the info…thanks!