I am confused, just get a scart cable and a scart to hdmi. Done.
Scart supports a bunch of TV image formats (composite, svideo, rgb etc..). In
All the TIs, Amiga, Amstrad, etc... Work ootb. You can find those converters for a few bucks on ebay. If you want to get fancy buy yourself an OSSC to get a really good image quality.
this wouldn't work fine with a Amiga. It supports some video modes that can be displayed on a TV. So needs a Commodore monitor or a scan doublet.
Also, the video output of some computers barely get in the standard. Yes, an analog TV can handle it fine, but try again on digital. I have a composite/SCART to VGA and can't sync correctly the composite output of my Spectrum +2. However, the same output it's handled correctly on my Commodore monitor
All the TIs, Amiga, Amstrad, etc... Work ootb. You can find those converters for a few bucks on ebay. If you want to get fancy buy yourself an OSSC to get a really good image quality.