You'll be shopping for an HDMI to [whatever your TV has] adapter.
Hopefully [whatever your TV has] includes Component video - the 5-cable interface. If all it has is Composite video - the 3-cable interface, then I would recommend replacing the TV instead of spending more to keep it on life support.
Try to buy it from a place with good return privileges because these devices are a bit hit-and-miss.
And avoid the really cheap things that are basically just a cable. Those only work on a very limited number of devices that can put analog video on an HDMI connector.
An HDMI to Analog (Composite Video, Stereo Audio) adapter will work fine. However, it has limitations. You are forced into 16:9 widescreen anamorphic mode. This is fine if the program is widescreen to begin with; it will be letterboxed on a 4:3 CRT. But if you are watching native 4:3 programs, it will squeeze the square image into a rectangle with black bars on the sides. You are also limited to stereo because analog outputs can't carry a Dolby Digital stream. If you get an older Roku with analog outputs, you can change to 4:3 native output, everything will display correctly and skip the HDMI adapter. But that introduces some other limitations such as price, menu slowdown, and/or streaming channel compatibility.
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